Thanks for the suggestions, however, I figured out the problem. Yes, BarData had to be marked as serializable, but even though BarCollection is derived from CollectionBase which is supposedly already serialized, I still have to add the [Serializable] attribute above that class as well. This is probably something that is glaringly obvious to anyone that knows anything about remoting ... but did I mention that this is the first day that I've tried it? :-D Thanks for the replies! Give me one more medicated peaceful moment