10 patients with the acquired immunodeficiency syndrome whose respiratory failure due to Pneumocystis carinii pneumonia (PCP) was deteriorating rapidly had 7 days of intravenous methylprednisolone added to their antibiotic regimen. 8 similar patients were treated with antibiotic therapy alone. 9 of the 10 methylprednisolone-treated patients survived their episode of PCP, compared with 2 of the 8 conventionally treated patients. Clinical improvement was evident within 2 days of the start of steroid therapy, and in none of the 10 patients did clinical deterioration or recurrence of PCP occur on cessation of steroid therapy. In 1 steroid-treated patient disseminated herpes zoster developed 2 days after discontinuation of methylprednisolone. Methylprednisolone seems to be a useful adjunctive therapeutic agent for patients with AIDS in whom Pneumocystis carinii is the sole respiratory pathogen.