Three types of rubella vaccine and a saline placebo were given to 748 young adult female students of the University of Michigan. Approximately 95% of those without prior antibody developed hemagglutinationinhibiting antibody one month after receiving any of the three vaccines. The only reaction significantly more common among vaccinees than controls was arthralgia. Rates of arthralgia in the seropositive placebo recipients were not significantly different from those of seropositive vaccinees. The three vaccines could be ranked for their capacity to produce arthralgia in seronegative subjects. Increased age was strongly associated with the likelihood of development of arthralgia. Among seronegative subjects, joint pain was 5.9 times more common in women 25 years and older than in women 19 to 24 years of age. In the latter group, the reactions were all mild.