Seventy healthy veterinary students with no previous history of rabies vaccination were inoculated either with human rabies immune globulin (HRIG) alone, human diploid cell strain (HDCS) vaccine alone, or combinations of both. HRIG, prepared either at the Lister Institute or by Cutter Laboratories, was inoculated (20 i.u./kg) on day 0, vaccine was inoculated on days 0, 3, 7 and 14 either in 0.1 ml doses intradermally (i.d.) or in 1.0 ml doses intramuscularly (i.m.). Neutralizing antibodies were measured by the mouse neutralization test on samples taken from each group of 10 volunteers on days 0, 1, 2, 3, 7, 10, 14, 21, 30, 50 and 90. The treatments were well tolerated and no serious reactions were seen. Antibody estimations, as yet incomplete, indicate that in those subjects receiving HRIG alone, low levels of antibody were detectable in most but not all cases after 24 hours; peak titres (0.16 i.u./ml : 1 in 7.2) were observed on days 2 and 3 and became undetectable after 30 days. Most subjects receiving vaccine and HRIG also had detectable antibody at 24 hours and all had antibody by 48 hours. Peak titres (GM +/- 18 i.u./ml) were recorded at 21 to 30 days. The response to vaccine administered by either route does not appear so far to be markedly suppressed by HRIG.