Periodic rabies booster injections are recommended for persons who are at continued risk of rabies exposures, but literature on booster intervals is not comprehensive. We recruited bat workers who received rabies vaccinations between September 2002 and March 2003 either as a primary rabies vaccination course (primary group) or rabies booster vaccination (secondary group). From September 2004, those bat workers in the primary group had two blood tests to determine their rabies antibody level; one immediately prior to their first booster vaccination and one approximately one month after the booster vaccination. Bat workers in the secondary group had one blood test, approximately two years after their last booster vaccination. Overall, 185 bat workers participated in the study: 145 in the primary group, 40 in the secondary group. Sixteen (11.1%) in the primary group were below the minimum recognized rabies antibody level of 0.5 IU/ml prior to their first booster vaccination; all were above this level one-month after their booster. All bat workers in the secondary group had a rabies antibody level above 0.5 IU/ml. In the primary group, age of the bat worker at primary immunization and rabies vaccine type were significantly associated with antibody response to the rabies booster. We recommend that the first rabies booster vaccination is given one year after the primary course and subsequent boosters are given every three to five years thereafter.