A 7-day infusion of prostaglandin E1 (PGE1), an immunomodulator, was evaluated in a prospective, randomized, placebo-controlled, double-blinded trial in surgical patients with the adult respiratory distress syndrome (ARDS). The drug seemed to improve pulmonary function--only two PGE1 patients died with severe pulmonary failure compared with nine placebo patients (p = 0.01). Survival at 30 days after the end of the infusion--the predetermined end point of the study--was significantly better in the patients given PGE1 (p = 0.03), with 15 of 21 PGE1 patients (71%) alive at this time compared with seven of 20 placebo patients (35%). Improvement in overall survival in the PGE1 patients did not reach statistical significance (p = 0.08). Overall survival in patients initially free of severe organ failure, however, was significantly better in the PGE1 patients (p = 0.03). Of the six PGE1 patients free of severe organ failure at time of entry, all survived to leave the hospital; of the 10 placebo patients initially free of severe organ failure, four survived. The drug had no serious side effects and did not potentiate susceptibility to infection. PGE1 is a promising agent for the treatment of ARDS.