Recurrence of adverse events, the effect of site of injection, and concurrent administration of oral polio vaccine (OPV) and hepatitis B vaccine (HBV) on reactogenicity were assessed in recipients of two acellular pertussis vaccines given in combination with diphtheria and tetanus toxoids (DTaP), one whole-cell DTP vaccine (DTPwc) and one DT vaccine during a double blind, randomized, controlled clinical trial. Local and systemic side reactions were more likely to recur after the administration of DTaP and DT compared with DTPwc. In all vaccine groups, injection in the buttock was associated with a lower rate of common adverse events compared with injection in the thigh, while simultaneous administration of OPV and/or HBV did not increase the risk of onset of side reactions.