FOR THE past several years, the major efforts of our laboratory have been concerned with the development of attenuated rubella virus strains, the production of experimental vaccines, and the clinical testing of these preparations in man.1-4 During the course of these studies it became essential to develop methods for isolation, identification, and quantitative measurement of virus as well as to develop tests which would serve as indicators of virus modification. Now, with the successful testing of vaccines prepared in a variety of avian and mammalian cells, our attention has turned to procedures which can be used in the monitoring of licensed live rubella vaccines. In general, many of the procedures established with live polio, measles, and mumps virus vaccines5 can be employed. However, one must use specific tests for rubella vaccines with respect to virus identity, quantitation of antibodies, vaccine potency measurement, and markers of virus attenuation. This