The paper presents the heuristic-numeric system AZEOPERT, a tool for predicting azeotropic behaviour. The system combines databases, numeric routines and heuristic rules. First AZEOPERT searches in a database with appr. 20,000 entries. If this search is not successful numeric routines are provided to estimate azeotropic behaviour and data. The third part of the consulting system uses heuristic rules which were derived from case studies. AZEOPERT can be used as a stand-alone system as well as part of a total environment for process synthesis called PROSYN.