A reproducible and sensitive rubella plaque neutralization test was established utilizing a Japanese, live, attenuated vaccine strain (KRT‐Kitasato, GMK 4/RT 36/RK 1) in a rabbit kidney cell line (RK‐13). Rubella strain, cell line derivation, addition of complement and temperature of incubation were all critical to the efficiency of plaque formation. Two hundred sera from 25 children collected longitudinally following rubella vaccination with HPV77DE5 were tested for rubella antibody by three different assays: 1) plaque neutralization, 2) hemagglutination inhibition, and 3) enzyme linked immunoadsorbent assay by commercial kit. Plaque neutralization antibody appeared more slowly after immunization than that determined by hemagglutination inhibition, but persisted in all 22 successfully immunized children over a five to seven year period. The same 22 children had a rise in hemaggulutination inhibition antibody, but lost detectable antibody five to seven years after vaccination. Only 21 children seroconverted by enzyme immunoadsorbent assay. Nine of these lost detectable antibody by five years.