In a field trial 181 high risk persons of both sexes between ages of 2--71 years were prophylactically vaccinated against rabies with the beta-propiolactone inactivated rabies-vaccine (hdc) mrc-5. 1 ml of vaccine was administered intramuscularly on days 0, 7 and 21. Serum samples were collected on days 0, 7, 21 and 35. Neutralizing antibody titers against the rabies virus were determined in the rapid fluorescent focus inhibition test, 7 days after the first injection measurable titers of antibodies were found in all sera with one exception. On day 21 all persons showed a 100% seroconversion with a mean titer of 1:1000 (8,3 IU/ml). On day 35 the final mean titer measured 1:2400 (20 IU/ml). Major side effects during the prophylactic vaccination were not observed.