Clinical experience with the Rubacell passive hemagglutination (PHA) test over a one-year period has shown the test to be a rapid, reliable, and economical method for determining antibody to rubella. The data from two separately administered rubella proficiency surveys showed 100% correlation between the PHA and the hemagglutination inhibition (HI) qualitative results with 24 reference specimens. Also, the PHA titers appeared to be generally higher than the HI in these specimens and in the sera of immune individuals. The efficacy of detecting HI antibody in the absence of PHA antibody as an indication of recent infection was compared to the HI paired sera method and to a rubella-specific immunoglobulin M (IgM) test based on protein A absorption. From the results obtained with the sera of 76 rubella patients, the efficacy of the three diagnostic methods was of the following order: protein A IgM test greater than positive HI/negative PHA greater than HI paired sera method.