A Randomized, Double-Blind, Placebo Controlled Study of l-Leucovorin in Combination With Trimethoprim / Sulfamethoxazole in the Therapy of Pneumocystis Carinii Pneumonia in Patients With the Acquired Immunodeficiency Syndrome

Inclusion Criteria Patients must have the following: * Diagnosis of PCP. * Fit the CDC definition of AIDS. * Be receiving intravenous or oral trimethoprim / sulfamethoxazole (Bactrim, Septra) in doses of = or \> 15mg/kg/day of the trimethoprim component. * Be receiving = or \< 48 hours of trimethoprim / sulfamethoxazole (TMP / SMX) prior to randomization. * Must sign informed consent in accordance with FDA guidelines. Exclusion Criteria Co-existing Condition: Patients with the following conditions or symptoms are excluded: * Cannot take oral medications. * Require continued administration of anticonvulsant agents such as phenytoin, phenobarbital or primidone. Concurrent Medication: Excluded: * Continued administration of anticonvulsant agents such as phenytoin, phenobarbital or primidone. Patients with the following are excluded: * Cannot take oral medications. * Require continued administration of anticonvulsant agents such as phenytoin, phenobarbital or primidone. Prior Medication: Excluded: * \> 48 hours of trimethoprim / sulfamethoxazole prior to randomization.