The different enzyme-linked immunosorbent assays (ELISA), a fluorescence immunoassay (FIAX), and a hemolysis-in-gel test (HIG) were examined for sensitive detection of specific antibodies in sera of persons with acute and previous rubella infection. In comparison to hemagglutination inhibition (HI), all tests were able to detect previously formed rubella antibodies. In sera of patients with acute rubella infection, only the FIAX system showed always positive results. Nevertheless, it remains unclear, if these findings are due to a higher sensitivity of the FIAX system or are possible non-specific results. In some cases, however, this test system failed to detect significant titre rises seen in HI, because it showed high antibody titres already in the first serum sample.