In Reply. — The restriction of viral replication (as measured by decreases in levels of serum p24 antigen), improved immunologic status, delays in the progression of human immunodeficiency virus disease, and prolongation of the disease-free interval seen with zidovudine therapy are associated with long-term survival benefits. 1 The prevention of Pneumocystis carinii pneumonia with sulfamethoxazole and trimethoprim has also been associated with prolonged survival in patients with acquired immunodeficiency syndrome—related Kaposi's sarcoma 2 and is most likely related to the prevention of P carinii pneumonia. However, it seems unlikely that prophylaxis for P carinii pneumonia alone would achieve the same survival benefits as found with zidovudine therapy. Nonetheless, it is possible that survival benefits conferred by zidovudine may be improved with the addition of an effective prophylactic agent. The use of prophylaxis for P carinii pneumonia in the long-term follow-up of subjects enrolled in the double-blind, placebo-controlled trial was at the