Antibody responses following primary vaccination with 1.0 ml of intramuscularly (im) or 0.1 ml of intradermally (id) administered human diploid cell rabies virus vaccine were observered for two years. Three primary doses of vaccine were given to 77 volunteers on days 0, 28, and 56. An antibody response was detected in all vacinees after a single dose; at one month, the response in the group that received vaccine id was identical to that in the group that was given vaccine im, although only 1/10th of the dose of vaccine was used. After the second and third doses, the antibody responses were higher with the primary im regimen; this difference was significant at two, three, and 12 months when the geometric mean titers of antibody were twofold higher for im than for id vaccination. The antibody responses to a booster dose of vaccine administered to randomly grouped volunteers by the subcutaneous or id route at six, 12, or 24 months were similar irrespective of the method of primary immunization but were greater with increasing intervals between primary and booster doses.