HIV infected patients (88% men and 12% women) with suspected (but no history of) PCP and no PCP-specific prophylaxis or treatment given for more than 48 hours. These individuals had a mean age of 33 years (range 18-55),78% were homosexual, 14% were intravenous drug users, 8% were infected by HIV through blood transfusion or heterosexual intercourse, 60% were smokers and 30% were nonsmokers.