This paper introduces Pact, a new model for parallel heuristic programming on MIMD machines. Designed and implemented as an integrated tool environment, Pact allows the user to develop and test (1) new distributed artificial intelligence applications, (2) new parallel heuristic search strategies and (3) new dynamic allocation algorithms. lar design and layer abstraction of Pact offers to the user features such as a powerful programming expressiveness, software modularity, portability and scalability. Three different prototypes of Pact have been implemented and tested in programming environments such as C-iPSC/2, Strand-Sun and Strand-C-Sun. R