The authors present data obtained from the study of sera in order to determine antibody leveis for rubella in Rio de Janeiro city, during the period 1970/1975. These sera induded mainly pregnant women having had contact with suspect and clinically defined cases of the disease. Among the group studies, 2155 cases of pregnants which had more complete data were analized with the purpose of stablishing immunity degree before contact and risk levei for the concept. It was found that 84,4% of these pregnants had rubella circulating antibodies and 8,1% of them reached leveis equal or more than 1/320, suggestive of recent infection. Serologic conversion was obtained in 1,2%, firming present infection. Analysis of data refering to notified cases of rubella during the period from 1965 to 1974 showa greater incidence during the secondsemester, as well as two outbreaks of the disease which had occurred in 1968 and in 1974.