Between January 1975 and December 1977 the Center for Disease Control treated 255 persons with the human diploid cell strain rabies vaccine who did not have development of an antibody titer to duck embryo vaccine (DEV) or who were at risk for having a serious reaction to DEV. Two hundred eighteen persons were treated postexposure, and 37 persons were treated preexposure. The antibody response to the vaccine was excellent, and the reaction rates were low. No person treated has had development of rabies. This study corroborates other studies that suggest that the human diploid cell strain rabies vaccines are safe and induce excellent antibody titers to rabies.