The use of trivalent equine antitoxin in treating foodborne botulism has not been adequately assessed. One hundred thirty-two cases of type A foodborne botulism reported to the Centers for Disease Control in the period from 1973 to 1980 are reviewed to evaluate the effect of antitoxin therapy and other factors on the outcomes of patients with botulism. The fatality rates were higher in patients over 60 years old and in those who were index patients (the first or only patient in an outbreak). The clinical course was longer in patients over 60 years old, patients whose incubation period was less than 36 hours, and index patients. Patients who had received trivalent equine antitoxin had a lower fatality rate and a shorter course than those who did not receive antitoxin, even after controlling for age and incubation period. Patients who received antitoxin in the first 24 hours after onset had a shorter course but about the same fatality rate as those who received antitoxin later. These results suggest that trivalent antitoxin has a beneficial effect on survival and shortens the course of patients with type A botulism.