- Unequivocal diagnosis of Pneumocystis carinii pneumonia (PCP) by morphologic confirmation of three or more typical P. carinii organisms in sputum, bronchoalveolar lavage fluid, or lung tissue obtained by transbronchial or open-lung biopsy within 3 days before or after randomization. If morphologic confirmation is not possible prior to therapy, patients may be randomized if the investigator believes there is a high suspicion of PCP based on clinical presentation. If morphologic diagnosis cannot be established within 6 days of randomization, the patient will be withdrawn from study therapy. Resting (A-a) DO2 < 30 torr on room air. Patient, parent, guardian, or person with power of attorney gives informed consent.