Pneumocystis carinii pneumonia (PCP) is a highly frequent cause of morbidity and mortality in immunocompromised subjects, particularly in HIV-infected ones. The biology of P. Carinii is poorly understood because of the lack of reliable synthetic media or adequate cell lines to grow this opportunistic pathogen in continuous culture. We reported the suitability of the MDCK (Madin Darby Canine Kidney, ATTC CCL 34) cell line to support the temporary microorganism's growth in vitro and the experimental pharmacological trials, in comparison with the HEL 299 cell line, used as reference standard.