A comparison was made of the general and local reactions and the antibody titers produced in 123 patients given injection of duck-embryo rabies vaccine and 127 patients given brain—tissue rabies vaccine (Semple). The results indicate that duck-embryo rabies vaccine stimulates an earlier production of antibodies than Semple vaccine and that the range of antibody titers between the 11 th and 15th days is not significantly different. Booster effects were obtained readily with both vaccines. In this study the complication of encephalomyelitis did not occur after the use of the duck-embryo vaccine but did occur in two patients who received the vaccine containing brain tissue. The recommendation that duck-embryo vaccine supplant the use of brain-tissue vaccine for prophylaxis of rabies seems to be justified.