Studies concerning the application of membrane distillation (MD) for the concentration of spent solution from heparin production have been reported. The experiments were performed with polypropylene capillary membranes. These membranes had pore sizes with a nominal and maximum diameter of 0.2 mu m and 0.6 mu m, respectively, and 73% porosity. A rapid flux decline was observed during the MD process of wastewater concentration as a consequence of both fouling and scaling phenomena. Boiling of wastewater followed by filtration permitted the separation of the foulants in the form of a deposit. Such pretreated feed was concentrated by the MD process without a flux decline. This process resulted in the production of pure water with electrical conductivity in the range of 5-10 mu S/cm and brine. The presence of Pseudomonas and Streptococcus faecalis bacteria and Penicillium and Aspergillus fungi was detected in the concentrated wastewater. The polypropylene membranes used did not reject Streptococcus faecalis bacteria; hence, they were detected in distillate.