A low rate of seroconversion to hepatitis B vaccine is reported. This occurred in healthy hospital employees from two separate institutions. A total of 236 individuals were evaluated in this study and only 53% or 124 persons developed protective levels of antibody to hepatitis B surface antigen following a complete vaccine series. In one hospital, 30% of the vaccine recipients developed antibody but not to a protective level. Employees who received the entire series in the arm or in the arm and buttock (mixed) had a significantly greater number of responders than employees who received the entire series in the buttock (P less than .05). Recipients aged 50 to 59 years had a significantly lower response rate to the vaccine (P less than .05). There was no correlation with the vaccinee's sex or the timing of the second injection. Vaccine was noted to have frozen in one hospital and accounted for some loss of antigenicity. This failure to respond to the vaccine has necessitated the use of booster injections of vaccine and continued antibody monitoring.