When 42 sera with low or inconsistent levels of haemagglutination-inhibiting (HAI) antibodies were tested by single radial haemolysis (SRH) radioimmunoassay (RIA), and enzyme-linked immunoassay (ELISA), RIA was shown to be the most reliable test for detecting low levels of antibody. SRH, however, was found to be an acceptable alternative screening test for rubella antibodies and was more reliable than HAI. Although SRH plates prepared in our own laboratory failed to detect antibodies in six sera, in five of the six, antibodies were only at a low level (RIA titre 1:20-1:80). OriVir plates (Orion Diagnostica, Finland) failed to detect low levels of antibody in only three sera. There were six (14.3%) sera which were false positives in the HAI test. These women were shown to be seronegative by radioimmunoassay and, when three of these six volunteers were vaccinated, they developed a typical primary immune response which resembled that developed by 43 seronegative women following vaccination. Fifteen of the young women with consistently low HAI titres and one woman who was seronegative by HAI but seropositive by RIA and ELISA were subsequently vaccinated. Six (37.5%) of these women showed no significant rise in titre by any of the tests employed, while ten had a significant rise in titre, detected by at least one test, with a low level of rubella-specific IgM detectable in one.

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A rapid simultaneous enzyme-linked immunosorbent assay (ELISA) using monoclonal antibodies was investigated for herpes simplex virus (HSV) detection. All HSV isolated (n = 127) were detected, whereas no response was obtained with HSV negative preparations. Equivalent results were obtained from 275 of 277 clinical specimens in the monoclonal ELISA and in an ELISA using polyclonal antibodies, confirming that appropriately selected monoclonal antibodies may be as efficacious as polyclonal antibodies in antibody-based assays. In clinical specimens, the rate of HSV detection (sensitivity) relative to tissue culture isolation was low for both assays, and the major factor responsible for this was the low concentration of virus present in some specimens. The sensitivity of ELISA obtained in routine use varied with different panels of unselected specimens and was related to the speed of development of the cytopathic effect. These results emphasise the need for caution in assigning a definitive sensitivity level to ELISA tests evaluated on different panels of specimens.