To evaluate the safety and effectiveness of trimetrexate (TMTX) given at increasing doses along with the leucovorin calcium (LCV) for treating Pneumocystis carinii pneumonia (PCP) in AIDS patients TMTX is an experimental new drug which is effective for treatment of PCP, but has been given to only a few patients. Therefore it is not certain if TMTX is better, the same as, or not as effective as conventional drugs against PCP.