Abstract A Formalin-inactivated mumps virus vaccine was prepared by concentrating infected allantoic fluid by means of the Sharples centrifuge. The vaccine material, in a dilution of 1:10, was used satisfactorily for skin testing of 125 individuals. One hundred of the same individuals were vaccinated, using different doses at different time intervals, and an appreciable increase in antibody levels was observed, as judged by complement fixation tests. Skin testing and complement fixation seem to be of comparable value for the determination of susceptibility. A tentative schedule of vaccination against mumps is presented.