Purified Rubella antigen is coated on the surface of microwells. Diluted patient serum is added to the wells, and the Rubella IgM- specific antibody, if present, binds to the antigen during incubation. After washing the wells to remove unbound sample, antibody to human IgM conjugated with horseradish peroxidase (HRP) is added and incubated at 37