Software has been developed which permits the quantitation of monoclonal antibodies secreted by B cell hybridomas. This program does not require the user to enter a large number of complex parameters and can be easily used without any previous computer experience. It fits all the experimental and standard curves by determining overlapping linear domains using the linear least-squares method. The program is based on logarithmic interpolations for determining Ig concentrations comparing experimental samples to Ig concentrations in standards. It provides a complete print-out of the data with editing options and is written in BASIC EDEX 4.0 Commodore computer language. It permits the accurate quantification of minute amounts of monoclonal antibodies and can be used to detect the inhibitory or enhancing effects of lymphokines or cytokines on Ig secretion by hybridoma B cells.