An automated microparticle enzyme immunoassay (IMx Rubella IgG Antibody Assay; Abbott Laboratories, North Chicago, Ill.) was compared with a conventional enzyme-linked immunosorbent assay (ELISA) for detection of rubella-specific immunoglobulin G (IgG) in 400 consecutive antenatal patients. There was complete agreement between the two tests in this population, which had a positivity rate of 99% for rubella-specific IgG antibodies. The performance of the IMx was also evaluated at the cutoff zone by assaying 64 selected antenatal serum samples with low or negative rubella antibody titers as determined by ELISA. Overall, the IMx was found to be a specific, sensitive assay for the detection of rubella-specific IgG and is virtually fully automated for easy performance.