We sought to determine the incidence of infection with hepatitis B virus (HBV) amongst hospital employees over a 10-year period and to assess the extent and efficacy of vaccination against HBV in this population. In 1984 a cohort of 301 hospital employees was tested for hepatitis B surface antibody (anti HBs), hepatitis B core antibody (anti HBc), and hepatitis B surface antigen (HBsAg). Ten years later, 160 (53%) of these workers remained at the hospital and were re-tested. In addition, they were tested for hepatitis C virus antibody (anti HCV). Records of the hospital vaccination program were inspected to determine the rate and effectiveness of vaccination in these workers. Over the ten year period two of the 160 retested workers (1.25%) had sero-converted to anti HBc positive, yielding an incidence density of 0.27 cases per 100 person-years exposed in unvaccinated workers. While the overall seroprevalence of anti HBc did not change significantly between 1984 (81/301, 27%) and 1994 (39/160, 24%), it was much greater than that of the general population (10%). A significantly greater percentage of Jews of Sephardi ancestry (22/65, 34%) were positive for anti HBc than those of Ashkenazi ancestry (15/90, 17%, P < 0.05). In addition, doctors were found to be less likely to be anti HBc positive than nurses (4% vs. 25%, respectively, P < 0.01). Two cases of anti HCV positivity were discovered yielding a prevalence of 1.25% in the 1994 cohort as compared to 0.15% in the population of healthy blood donors. Of the 93 employees of the 1994 cohort eligible for vaccination (i.e., anti HBc-negative and employed in an occupation involving potential exposure to HBV), 53 (57%) had received vaccination and showed protective antibody titers (anti HBs > or = 10 i.u./ml). 17/52 workers with documented vaccinations (33%) did not have detectable antibody levels one to eight years after vaccination. In conclusion, the seroprevalence of anti HBc and anti HCV is significantly higher in this cohort of hospital employees than in the general population. The relatively low vaccination rate among at-risk personnel emphasizes the need for more effective vaccination programs.