Studies of human globulin immune to rabies virus before licensure showed that it suppressed active antibody responses when individuals received 16 doses of duck embryo vaccine but not when they received 23 doses of duck embryo vaccine. Prospective surveillance of use of human globulin immune to rabies virus since licensure in 1974 has revealed that 40% of persons who receive 14–16 doses of duck embryo vaccine have low or undetectable antibody responses 3090 days after initiation of the series. Ten percent of individuals receiving 21–23 doses of duck embryo vaccine have inadequate antibody responses, a percentage not significantly different from that found in recipients of 14 doses of vaccine alone. Human globulin immune to rabies virus has also been used for treatment of one case of clinical human rabies; this use was based on the observation that antibodies to rabies virus in serum do not develop until after the seventh day of clinical illness, and antibodies are absent from spinal fluid as long as 19 days after onset of symptoms. Intracranial pressure and neurological function remained stable after administration of human globulin immune to rabies virus, but two days after initiation of therapy, the patient died of progressive pulmonary dysfunction and tension pneumothorax.