Rubella vaccine, the Cendehill strain, was evaluated clinically and by measuring the hemagglutination-inhibition antibody response in the sera of both children and young women. In both groups of susceptible individuals, an antibody response occurred in over 99 per cent. The titer in children has remained fairly constant for at least 9 months. The Cendehill vaccine produces virtually no side effects in children and a low incidence in young women. Rubella virus was isolated from the nasopharynx of one half of the vaccinees, but there was no evidence of communicability. Eighteen months after vaccination, 4 children were challenged by inoculation with unattenuated rubella virus; none had any clinical manifestations of rubella. Rubella vaccine, the Cendehill strain, was evaluated clinically and by measuring the hemagglutination-inhibition antibody response in the sera of both children and young women. In both groups of susceptible individuals, an antibody response occurred in over 99 per cent. The titer in children has remained fairly constant for at least 9 months. The Cendehill vaccine produces virtually no side effects in children and a low incidence in young women. Rubella virus was isolated from the nasopharynx of one half of the vaccinees, but there was no evidence of communicability. Eighteen months after vaccination, 4 children were challenged by inoculation with unattenuated rubella virus; none had any clinical manifestations of rubella.