BACKGROUND: The test for the anti-rubella IgM Ab (R-IgM) is important in early pregnancies because therapeutic termination may be considered depending on the results. METHODS: The subjects consisted of 52 pregnant women with positive or equivocal R-IgM by Cobas Core Anti-Rubella IgM EIA test (Roche, Basel, Swiss) between January 1997 and July 2000. Three different EIA methods such as the Enzygnost Anti-Rubella-virus/IgM test (DADE Behring, Marburg, Germany), the AxSYM Anti-Rubella IgM test (Abbott, USA), and the IMx Anti-Rubella IgM test (Abbott, USA) were simultaneously performed on 44 specimens as well as the Cobas Core Anti-Rubella IgM EIA test. RESULTS: Among 52 pregnancies, 9 (17%) experienced an artificial abortion due to positive or equivocal R-IgM result. The clinical symptoms associated with rubella infection were observed in 3 cases and the persistent R-IgM positivity was noted for more than 1 year in 4 cases. The concordance rate between 4 different EIAs was 41%. When performed with serial diluted pool and 3 sera, the results of Cobas Core were similar to those of AxSYM, IMx and Enzygnost. The R-IgM were detected one titre higher in diluted sera performed by IMx and Enzygnost than those of Cobas Core and AxSYM. CONCLUSIONS: For pregnancies with positive or equivocal R-IgM, it is recommended that results should be interpreted with caution, considering the possibilities, such as a persistent R-IgM response and discrepant R-IgM depending on the different EIA methods.