Inclusion Criteria

Patient must:

• Have Pneumocystis carinii pneumonia (PCP) that has not been treated for current episode. PCP must be documented by observation of > 1 cluster of organisms in sputum, bronchial secretion, or lung tissue.
• Have clinical symptoms of respiratory disease or radiologic abnormalities.

Exclusion Criteria

• Patient cannot have significant emotional disorder.

Concurrent Medication: Excluded:

• Drugs likely to be bone marrow toxic.
• Investigational drugs.

Prior Medication: Excluded:

• Three patients in each group cannot have had zidovudine (AZT) for at least 2 months prior to administration of trimetrexate.