Abstract. The system described in this report is comprised of a low voltage power supply, cassettes containing buffered agar, electrodes (and a viewer). The rabbit anti-HAA is balanced to detect reactions ranging from weak to prozone. In double-blind studies, the test results agreed closely with the results obtained with specimens from hepatitis cases after antigen concentrations followed by double diffusion and also with the results of regular counterimmunoelectrophoresis in which blood donors had been studied. Antibody and antigenic variants can also be detected.