In 1967-1968 a trial of "Cendehill strain" rubella vaccine was initiated in a group of 3 to 22 year-old prescreened seronegative girls, most being between 8 and 16 years of age. Sera from the vaccinees were taken at regular intervals during a period of 8 to 10 years. The evolution of the antibodies was followed over this period. No antibody titer change was observed in 75 to 78% of the sera. A four fold increase was shown in 6 to 10% and a four fold decrease in 15% of the vaccinees. All sera still showed a positive titer at the end of the period. The importance of these results for the final objective of rubella vaccination will be discussed.