A double-blind, controlled, randomized trial was conducted to evaluate the safety and immunogenicity of a new human rabies immune globulin (HTRIG). This product, manufactured by Pasteur Merieux Connaught, PMC, has undergone a heat-treatment step (10 h at 60 degrees C) and removal of mercurothiolate. The corresponding unheated product available from the same manufacturer (human rabies immune globulin, HRIG, IMOGAM RABIES[spr2]) was used for comparison. These two rabies immune globulins (RIGs) were administered either alone or in association with the human diploid cell rabies vaccine (HDCV, IMOVAX[spr2] RABIES, PMC) according to a standard, post-exposure rabies prophylaxis schedule. Sixty-four healthy adults were randomly assigned to four groups of 16 to receive either HRIG/placebo, HTRIG/placebo, HRIG/HDCV or HTRIG/HDCV. RIG was administered at the recommended dose of 20 IU/kg by three intramuscular (i.m.) injections in the gluteus. HDCV or placebo was given on day (D) 0, D3, D7, D14, and D28 into the deltoid by the intramuscular (i.m.) route. Any local reaction from D0 to D3 at the immune globulin injection site, and any systemic reaction from D0 to D42, were monitored by subject diaries. Rabies-neutralizing serum antibody levels were assessed by the rapid fluorescent focus inhibition test (RFFIT) before treatment and on D3, D7, D14, D28, D35, and D42. No serious adverse reactions and, in particular, no allergic-type reactions were reported. The safety profiles of HTRIG and HRIG were similar, except that complaints of pain, or tenderness at the injection site were half as common in the HTRIG group. Most of the local reactions were mild or moderate. After the administration of HTRIG/placebo or HRIG/placebo, 60% of subjects had detectable rabies antibodies levels, but by D42 all titres were below the seroprotective level (i.e. below 0.5 IU/ml). In the groups HTRIG/HDCV and HRIG/HDCV, the antibody titres rose markedly from D7, and reached a maximum value of 19 IU/ml (95% CI, 11 to 38 IU/ml) and 31 IU/ml (95% CI, 20 to 48 IU/ml), respectively, on day 14. All subjects who received RIG and vaccine maintained a protective antibody level from D14 to D42. No significant difference in immunogenicity results between these two groups (HTRIG/HDCV and HRIG/HDCV) was observed, and no interference of immune globulin with vaccine was reported. The safety and immunogenicity profiles of PMC HTRIG appear comparable with the current reference product. The heat-treatment step will enhance the safety by further reducing the probability of virus transmission through immune globulin treatment. The low levels of rabies antibodies obtained by intramuscular administration of either PMC HTRIG or of PMC HRIG support the recommendations that call for local infiltration of wounds with RIG.