Eflornithine (DFMO) was used to treat 31 AIDS patients with confirmed Pneumocystis carinii pneumonia who had clinically failed treatment with pentamidine, sulphamethoxazole-trimethoprim or both agents as their first-line therapy. Twenty-one of 31 (68%) responded to second-line treatment with 400mg/kg per day of eflornithine. Five patients discontinued treatment because of bone marrow toxicity. Eflornithine appears to be a useful salvage therapy in patients failing first-line treatments.