Between 1955 and 1987, 17 patients were examined at the Mayo Clinic shortly after exposure to silo gas. All exposures had occurred in conventional top-unloading silos. Acute lung injury occurred in 11 patients, 1 of whom died; early diffuse alveolar damage with hyaline membranes and hemorrhagic pulmonary edema and acute edema of the airways were found at autopsy. In one patient, hypoxemia and transient obstruction of the airways developed, but no pulmonary infiltrates were noted. One patient had symptoms for 5 weeks and diffuse confluent pulmonary infiltrates; many years later, chronic obstructive pulmonary disease developed (he had, however, been a heavy smoker before exposure). Bronchiolitis obliterans was not observed in the other patients, probably because of less severe exposure or early corticosteroid therapy. Prophylactic corticosteroid therapy is advised for workers who have been exposed to silo gas. The management of patients with established acute lung injury is reviewed. Previously unreported patterns of exposure to silo gas in conventional silos are described, and recommendations for avoiding exposure are suggested.