diff --git a/client-ts/Microsoft.AspNetCore.SignalR.Client.TS.Tests/HubConnection.spec.ts b/client-ts/Microsoft.AspNetCore.SignalR.Client.TS.Tests/HubConnection.spec.ts
index a2ec536e1f..aa7d05b871 100644
--- a/client-ts/Microsoft.AspNetCore.SignalR.Client.TS.Tests/HubConnection.spec.ts
+++ b/client-ts/Microsoft.AspNetCore.SignalR.Client.TS.Tests/HubConnection.spec.ts
@@ -387,6 +387,31 @@ describe("HubConnection", () => {
             // Expectation is connection.receive will not to throw
             connection.receive({ type: MessageType.Completion, invocationId: connection.lastInvocationId });
         });
+
+        it("can be canceled", () => {
+            let connection = new TestConnection();
+
+            let hubConnection = new HubConnection(connection, { logger: null });
+            let observer = new TestObserver();
+            let subscription = hubConnection.stream("testMethod")
+                .subscribe(observer);
+
+            connection.receive({ type: MessageType.StreamItem, invocationId: connection.lastInvocationId, item: 1 });
+            expect(observer.itemsReceived).toEqual([1]);
+
+            subscription.dispose();
+
+            connection.receive({ type: MessageType.StreamItem, invocationId: connection.lastInvocationId, item: 2 });
+            // Observer should no longer receive messages
+            expect(observer.itemsReceived).toEqual([1]);
+
+            // Verify the cancel is sent
+            expect(connection.sentData.length).toBe(2);
+            expect(JSON.parse(connection.sentData[1])).toEqual({
+                type: MessageType.CancelInvocation,
+                invocationId: connection.lastInvocationId
+            });
+        });
     });
 
     describe("onClose", () => {
diff --git a/client-ts/Microsoft.AspNetCore.SignalR.Client.TS/HubConnection.ts b/client-ts/Microsoft.AspNetCore.SignalR.Client.TS/HubConnection.ts
index a4a8451c90..7c4d819b05 100644
--- a/client-ts/Microsoft.AspNetCore.SignalR.Client.TS/HubConnection.ts
+++ b/client-ts/Microsoft.AspNetCore.SignalR.Client.TS/HubConnection.ts
@@ -6,7 +6,7 @@ import { IConnection } from "./IConnection"
 import { HttpConnection } from "./HttpConnection"
 import { TransportType, TransferMode } from "./Transports"
 import { Subject, Observable } from "./Observable"
-import { IHubProtocol, ProtocolType, MessageType, HubMessage, CompletionMessage, ResultMessage, InvocationMessage, StreamInvocationMessage, NegotiationMessage } from "./IHubProtocol";
+import { IHubProtocol, ProtocolType, MessageType, HubMessage, CompletionMessage, ResultMessage, InvocationMessage, StreamInvocationMessage, NegotiationMessage, CancelInvocation } from "./IHubProtocol";
 import { JsonHubProtocol } from "./JsonHubProtocol";
 import { TextMessageFormat } from "./Formatters"
 import { Base64EncodedHubProtocol } from "./Base64EncodedHubProtocol"
@@ -167,7 +167,14 @@ export class HubConnection {
     stream<T>(methodName: string, ...args: any[]): Observable<T> {
         let invocationDescriptor = this.createStreamInvocation(methodName, args);
 
-        let subject = new Subject<T>();
+        let subject = new Subject<T>(() => {
+            let cancelInvocation: CancelInvocation = this.createCancelInvocation(invocationDescriptor.invocationId);
+            let message: any = this.protocol.writeMessage(cancelInvocation);
+
+            this.callbacks.delete(invocationDescriptor.invocationId);
+
+            return this.connection.send(message);
+        });
 
         this.callbacks.set(invocationDescriptor.invocationId, (invocationEvent: HubMessage, error?: Error) => {
             if (error) {
@@ -280,7 +287,7 @@ export class HubConnection {
 
     private createInvocation(methodName: string, args: any[], nonblocking: boolean): InvocationMessage {
         if (nonblocking) {
-            return <InvocationMessage>{
+            return {
                 type: MessageType.Invocation,
                 target: methodName,
                 arguments: args,
@@ -290,7 +297,7 @@ export class HubConnection {
             let id = this.id;
             this.id++;
 
-            return <InvocationMessage>{
+            return {
                 type: MessageType.Invocation,
                 invocationId: id.toString(),
                 target: methodName,
@@ -303,11 +310,18 @@ export class HubConnection {
         let id = this.id;
         this.id++;
 
-        return <StreamInvocationMessage>{
+        return {
             type: MessageType.StreamInvocation,
             invocationId: id.toString(),
             target: methodName,
             arguments: args,
         };
     }
+
+    private createCancelInvocation(id: string): CancelInvocation {
+        return {
+            type: MessageType.CancelInvocation,
+            invocationId: id,
+        };
+    }
 }
diff --git a/client-ts/Microsoft.AspNetCore.SignalR.Client.TS/IHubProtocol.ts b/client-ts/Microsoft.AspNetCore.SignalR.Client.TS/IHubProtocol.ts
index 01fc2831dd..03859bbaaa 100644
--- a/client-ts/Microsoft.AspNetCore.SignalR.Client.TS/IHubProtocol.ts
+++ b/client-ts/Microsoft.AspNetCore.SignalR.Client.TS/IHubProtocol.ts
@@ -41,6 +41,10 @@ export interface NegotiationMessage {
     readonly protocol: string;
 }
 
+export interface CancelInvocation extends HubMessage {
+    readonly invocationId: string;
+}
+
 export const enum ProtocolType {
     Text = 1,
     Binary
diff --git a/client-ts/Microsoft.AspNetCore.SignalR.Client.TS/Observable.ts b/client-ts/Microsoft.AspNetCore.SignalR.Client.TS/Observable.ts
index e2ea7cb11e..eeaaf0c626 100644
--- a/client-ts/Microsoft.AspNetCore.SignalR.Client.TS/Observable.ts
+++ b/client-ts/Microsoft.AspNetCore.SignalR.Client.TS/Observable.ts
@@ -10,16 +10,38 @@ export interface Observer<T> {
     complete?: () => void;
 }
 
+export class Subscription<T> {
+    subject: Subject<T>;
+    observer: Observer<T>;
+
+    constructor(subject: Subject<T>, observer: Observer<T>) {
+        this.subject = subject;
+        this.observer = observer;
+    }
+
+    public dispose(): void {
+        let index: number = this.subject.observers.indexOf(this.observer);
+        if (index > -1) {
+            this.subject.observers.splice(index, 1);
+        }
+
+        if (this.subject.observers.length === 0) {
+            this.subject.cancelCallback().catch((_) => { });
+        }
+    }
+}
+
 export interface Observable<T> {
-    // TODO: Return a Subscription so the caller can unsubscribe? IDisposable in System.IObservable
-    subscribe(observer: Observer<T>): void;
+    subscribe(observer: Observer<T>): Subscription<T>;
 }
 
 export class Subject<T> implements Observable<T> {
     observers: Observer<T>[];
+    cancelCallback: () => Promise<void>;
 
-    constructor() {
+    constructor(cancelCallback: () => Promise<void>) {
         this.observers = [];
+        this.cancelCallback = cancelCallback;
     }
 
     public next(item: T): void {
@@ -44,7 +66,8 @@ export class Subject<T> implements Observable<T> {
         }
     }
 
-    public subscribe(observer: Observer<T>): void {
+    public subscribe(observer: Observer<T>): Subscription<T> {
         this.observers.push(observer);
+        return new Subscription(this, observer);
     }
 }