I am writing a WCF service that also needs to be able to support legacy clients. I want to send a file from the service to the client. The service method returns an object, lets call it a ServiceRtn object. The ServiceRtn class has a data member named FileBytes declared as a byte. The service uses File.ReadAllBytes to populate FileBytes. When stepping through the code I can see that FileBytes is populated correctly. The client assigns the return value of the service method to a ServiceRtn object. All of the other data members of the ServiceRtn object are as expected, but FileBytes is null. Can somebody tell me what I'm doing wrong? Thanks.