Serological antibody response for over a year to rubella live virus vaccination was examined by hemagglutination inhibition (HI) test and enzyme-linked immunosorbent assay (ELISA) of 22 seronegative and 25 seropositive sera of young women. In the seronegative group, some HI antibody response appeared first 2 weeks after the vaccination. A positive response of ELISA-IgM was first observed at 3 weeks, showing slowly declining values within the following year. Similarly, ELISA-IgG response occurred first and was positive 3 weeks later with gradual increases in both ELISA-values and positive ratios for 5 months. In the seropositive group, responses of both ELISA-IgM and -IgG were found within a few levels of ELISA-values from 2 weeks after the vaccination. Higher ELISA-IgM values observed after the natural infections than those following in the vaccination should be cited. These possibly show different amounts of viral antigens introduced in vivo. Reinfection of high HI antibody cases may be distinguished by small changes in the ELISA-value's pattern. When the above data are taken together, single measurement of ELISA-IgM does not seem to always be definitive and characteristic changes in positive patterns may be much more important in clinically diagnosing recent rubella virus infection.