Parents from four practices were surveyed to ascertain reactions of children to diphtheria-pertussis-tetanus (DPT) vaccine in the 48 hours after immunization. Vaccines were administered according to current recommendations. Responses were scored in three categories: temperature, behavioral changes, and local reactions. Questionnaires were returned by 1,232 (84.9%) patients. Only 7.0% reported no reaction, while 336 (27.3%) reported mild, 722 (58.6%) moderate, and 88 (7.1%) severe reactions. Over 50% experienced temperatures of at least 100 F, and 80% noted behavioral changes; 72.2% had local reactions. No encephalitis, seizures, or hospitalizations were reported. Reactogenicity was similar for the five immunizations of the recommended series and the two manufacturers evaluated. Reported reactions in the control group were significantly lower than in the study group. These reaction rates underline the need to reevaluate present DPT vaccines.