A simple and rapid technique for quantification of rubella virus is described. The specificity of the competitive enzyme linked immunosorbent assay (ELISA) was quantified by comparing the slopes and the Y intercepts of the curves obtained when viral antigen vs. control antigen was used. The curves were derived by plotting the absorbance ratio against the logarithm of the antigen concentration. The technique was reproducible, its sensitivity depending on the purity of the antigen used. In ELISA, when an antigen precipitated by ammonium sulfate was used, the sensitivity expressed in protein/ml was 7 ampersand-flag-changemu;g and when an antigen purified by sucrose gradient was used, 70 ng, whereas the limit of sensitivity in the standard technique of hemagglutination was only 38 ampersand-flag-changemu;g.
