EDPEPPS: An environment for optimal parallel software design. A performance oriented parallel program development environment called EDPEPPS is discussed. EDPEPPS integrates a graphical design tool, a simulation engine and a performance visualisation tool and supports the rapid prototype development of message-passing applications using the portable PVM communication library. The central module of the environment is the simulation engine using the commercial SES/Workbench software that allows performance analysis to be done without accessing the target platform. Thus, the user can measure easily the expected performance of different application prototypes to run on various target platforms. To ensure correct simulation results, a detailed PVM platform model library has been elaborated that is linked against the user application to be simulated. Beside the PVM message passing system, the model library incorporates information on the underlying system and hardware environment as well. The authors give a brief summary of the program development methodology supported by EDPEPPS and a short description of each individual tool comprising the system. Some validation results concerning the simulation model are presented as well.