An anticomplementary activity (ACA) assay on a microtiter plate combined with a computer-controlled plate reader and computerized calculation of the assay result is described. The assay is a simplified version of existing ones and can be used to assay immunoglobulins at low protein concentrations. The method detects the consumption of 0.13 CH50U, corresponding to anticomplementary activity of 7.5 CH50U/g protein. The assay has a coefficient of variation of 20.4%.