Voluntary reporting of vaccine reactions was intensified in a single large region for 7 years Anaphylaxis and collapse, convulsion, and neurological disorder were reported most frequently after diphtheria/tetanus/pertussis (DTP). The greater frequency of recorded reactions after DTP than after DT could have been due to bias caused by the adverse publicity accorded to pertussis vaccine, since no major difference was found when the immunisation histories of children admitted to hospital with such conditions were compared. No convincing evidence that DTP caused major neurological damage emerged from this large and lengthy study.