The immunogenicity and reactogenicity of a booster dose of enhanced potency inactivated polio vaccine (EIPV) were evaluated in 492 healthy 12 year old adolescents. The booster was administered at the same time as the HBV vaccine compulsory in Italy at this age. Blood samples and questionnaires on reactogenicity were collected over 9 months. Analysis of pre-vaccination immunity showed that 97.4% of the subjects were protected against all polio types, 1.9% were negative for two polio types and 0.6% for one. After vaccination 98.4% of the vaccinees showed a significant increase ( > or = 4 times) of antibody titre; the geometric mean titres (GMT) were markedly higher than before vaccination, particularly for poliovirus type 3. The polio booster dose did not affect HBV vaccination. An anti-HBs response > 10 mIU ml-1. (GMT = 2951 mIU ml-1) was observed in 781 (98.6%) of 792 vaccinees (492 given EIPV+HBV and 300 given only HBV) 9 months later. Only mild local and rare general reactions were noted for both the vaccines studied. These data confirm the suitability and efficacy of an EIPV booster dose and HBV vaccination in adolescents.