As part of a vaccination program which included about 30,000 children, 1,036 children were actively followed up to assess the reactogenicity of a combined DTPw-HB vaccine (Tritanrix-HB) under routine conditions. Vaccinations were given in accordance with the WHO schedule at 6, 10, and 14 weeks of age. Over 98% of the study population completed the course of 3 vaccinations. Local and systemic reactions to the vaccine were mostly mild and transient, and almost all had resolved by 3 days after vaccination. The most common systemic reactions were irritability, restlessness, and unusual crying. Only 3 infants had fever of > or = 40 degrees C after any vaccination. No serious adverse events were reported during the study. Most health workers taking part in the study thought that combined vaccines were better than separate vaccinations. Overall, these results show that the combined DTPw-HB vaccine used in the study was well tolerated and accepted under conditions of normal use.