Angular 2 / rxjs chaining HTTP calls
public createAccount(registrationRequest: CreateUserRequestModel): Observable&lt;SomeType&gt; {
  return this.apiService.post('api/register/account', registrationRequest)
    .flatMap(() =&gt; this.authenticationService.authenticate(registrationRequest.emailAddress, registrationRequest.password))
    .map(response =&gt; &lt;SomeType&gt;response.json())
    .catch(error =&gt; Observable.throw(error.json()));
}



@Tushar made a good point on code compactness, which can be applied to all arrow functions in the code.
TypeScript is about types. Try to not use any in return type definitions. Do define some return type and cast the result to it (see SomeType).
I'm not sure if you really want to do .catch(error =&gt; Observable.throw(error.json())) where it happens now or move it to the consumers side (e.g. .subscribe(() =&gt; {...}, error =&gt; this.handle(error))
reg is a bad name. Spell things out.