A new solid-phase assay system has been developed for the detection of irregular antibodies in plasma and serum specimens. By means of a magnetic indicator cell, we have established a sensitive and easy-to-handle antihuman globulin (AHG) test involving magnetic-mixed passive hemagglutination (M-MPHA). Comparative studies of M-MPHA with conventional AHG tests demonstrated that this is sufficiently sensitive and specific to detect irregular antibodies to red blood cells. Elimination of centrifugation in this test seems to open the way toward new standardization of solid-phase systems.