Although the efficacy of hepatitis B vaccines in patients under chronic hemodialysis treatment has been well documented, the persistence of immunity in this population remains largely unknown. In this study we have followed 60 hemodialysis patients up to 3 years after primary hepatitis B vaccination (four doses of recombinant hepatitis B vaccine; Engerix B, 20 mg/dose) to evaluate the persistence of immunity (as indicated by serum levels of antibody to hepatitis B surface antigen-anti-HBs-higher than or equal to 10 mIU/ml). Fourty-four (73%) patients developed anti-HBs levels above 10 mIU/ml after vaccination; the remaining 16 (27%) vaccinees were considered nonresponders and were given a booster dose that again failed to elicit an immunoresponse. After 3 years of follow-up, 18 out of 44 (41%) responders had no detectable anti-HBs levels in the serum (antibody loss occurring within 8 and 12 months in 3 cases, within 1 and 2 years in 13, and within 2 and 3 years in 2 other cases). When compared with the responders that lost their antibodies during the follow-up period, those who remained immunoreactive 3 years after vaccination was initiated were younger and had higher anti-HBs levels at 8 months of follow-up. Two hepatitis B virus infections were detected among nonresponders during the follow-up period. Based on these data, we conclude that patients undergoing chronic hemodialysis therapy not only have lower response rates to hepatitis B vaccination than healthy adults, but also that these are frequently transient.(ABSTRACT TRUNCATED AT 250 WORDS)