Abstract. Debugging parallel programs can be very time-consuming and tedious, because the multiplicity of communicating processes increases the complexity of a program and the probability of incorrect behavior. Solutions are provided by debugging tools, which try to offer meaningful ways to investigate errors and their original causes. The MAD environment is a debugging toolset, which focuses on parallel and distributed programs. This paper discusses the application of MAD to real-world programs with practicability and usability as the main goals. The observations are based on a series of debugging sessions conducted for a specific application of theoretical physics, with the opinions of the tool developer on one side and the view of the application developer on the other side.