This research explores the usefulness of control-flow versus interprocess communications information in documentation of concurrent processing programs. Programmer performance was examined on a modification task where modifications were made to either the data structure or the control flow of a program. The results suggest that for simple programs and simple modifications, it is not crucial whether interprocess communications or control-flow information is highlighted in the documentation format. For more complex problems, it would appear that detailed control-flow information is not necessary, and, in fact, may interfere with making the modification.