Groups of adult humans, previously unexposed to rabies and with no history of rabies vaccination, were inoculated with different schedules of phenolized inactivated vaccine and Flury strain chicken-embryo vaccine, with or without one inoculation of hyperimmune serum. Serum specimens of the inoculated individuals were studied for antibody up to the 28th day following the first inoculation of the vaccines and serum. The results can be summarized as follows:1. Passive antibody appeared in the blood-stream within one day following inoculation of hyperimmune serum. The antibody persisted at a good level for at least 10 days, but dropped slightly by the 14th day and was present in most individuals at the 21st day.2. There was a tendency for the antibody levels at 21 and 28 days to be lower in the phenolized vaccine plus antiserum groups than in those groups which received phenolized vaccine alone.3. Seven or 12 daily inoculations of phenolized vaccine alone produced antibody in most instances by the 10th day and persisted generally through the 28th day.4. Daily inoculations of phenolized vaccine produced a superior antibody response to that derived from the same total amount of vaccine given as a single inoculation.5. A single inoculation intramuscularly of Flury strain chicken-embryo vaccine of high egg-passage did not produce detectable antibody.6. The group which received hyperimmune serum followed by 12 daily inoculations of phenolized vaccine showed early and persistent antibody throughout the entire period of test. The antibody levels were comparable to those recently observed in man treated effectively with antiserum-vaccine combination after severe exposure to rabies.(9)