Mouse isohemagglutinins and leukoagglutinins have been detected and quantitated by a sensitive reproducible assay. The procedure measures intercellular dissociation and migration of centrifuged cells in capillary tubes by the force of gravity. The assay does not require high concentrations of developers such as dextran and polyvinylpyrrolidone, and appears to be equally sensitive to “complete” and “incomplete” antibody.