Building distributed systems is an inherently difficult and complex task. Modern middleware architectures assist developers ding abstractions that hide transport layer functionality. This paper argues that the development of such systems can be aided by the availability of appropriate, integrated tools. We discuss ways in which the building of such systems can be supported by development tools, focusing particularly on interactive testing and debugging mechanisms. A prototype system based on the BlueJ programming environment has been developed to support the development of Java RMI applications as a basis for further investigation. The tools developed as part of this prototype are presented and discussed. Categories and Subject Descriptors D.2.6 [Software Engineering]: Programming Environments integrated environments, interactive environments, programmer workbench; D.2.5 [Software Engineering]: Testing and Debugging General Terms Experimentation, Verification. Keywords Distributed Sys...