Passive immunization has proven an important complementary method for protection of an infected organism against rabies in the very first phase after virus contact. Passive-active immunization is by far superior compared to vaccination only. A few cases of human rabies after serovaccination in due time might be due to interference (immunosuppression) of active antibody formation after vaccination by passiively administered performed heterologous rabies immune globulin. This "interference phenomenon" can probably be explained as an imbalance of antigen and antibody in vivo, i.e. antigen masking and, hence, blocking of the immune reaction on its afferent branch. Both, 19S- and 7S- antibody moleculars, are able to induce interference. Whereas the old heterologous antisera from horse or mule, in an extremely high percentage, provoked moderate or severe side effects of such as urticaria, serum sickness, immune complex nephritis etc., the now available homologous Rabies Immune Globulin of Human Origin (RIGH) is very well tolerated, of long-lasting effectiveness and does not interfere with active antibody formation after application of HDCS-tissues culture vaccine, when an amount of 20 I.U./kg bodyweight of RIGH and 6 diseases of HDCS-vaccine on days, 0, 3, 7, 14, 30 and 90 (Essen schedule postexposure vaccination) is used.