During a mass diphtheria-tetanus immunization campaign in November 1975, more than 220,000 doses of diphtheria-tetanus toxoid, adult type were administered to adults throughout Alaska. In Anchorage, where more than 87,000 doses were given, a survey was conducted to determine the frequency of side effects. Postcard questionnaires were mailed to 2,000 randomly selected Anchorage residents; 467 questionnaires were returned by the post office as undeliverable, and 697 questionnaires were completed and returned. A follow-up survey was done of a random sample of the 836 non-responders. Of those responding, 57.8 per cent reported at least one reaction to the toxoids. The most frequent side effects were sore arm (42.7 per cent), swelling at the site of injection (34.8 per cent), and itching (24.2 per cent). Serious side effects occurred less frequently-swelling of the arm below the elbow (1.1 per cent) and abscess or infection (0.7 per cent). Of those vaccinated, 0.5 per cent saw a physician. There were no statistically significant differences in reaction rates by age group, except for sore arms. The jet injector produced more arm swelling at the site of injection, hives, and itching. More women than men reported adverse reactions, especially sore arm, swelling at the site of injection, and itching. Fear of adverse side effects should not preclude mass vaccination of adults. (Am. J. Public Health (69:246-249,1979.)