196 sera of children jrcm 2 schools of Guanabara were examined for the presence of HI Rubella antibodies. Only 24 samples turned out to be negative and from these susceptible children, o7ie. group has been vaccinated (vaccine Cendehill, R.I.T. Laboratory) and the other group has been left as control. By the second blood sample collection 100r'i conversion has been observed in the vaccinees. The high pre-vaccinal level of antibodies against Rubella observed in this trial suggests a broad circulation oj Rubella virus in the studied groups.