A sensitive and rapid assay for leukoagglutinating lectins has been developed. This assay utilizes neutral red-stained mouse lymphoma cells from the suspension cultured cell line BW5147. The agglutination of the stained cells can be monitored visually in a manner similar to that for conventional assays for erythroagglutinating lectins using erythrocytes. The activity of lekoagglutinating lectins that are not capable of agglutinating erythrocytes can be quantified by this assay. The utility of the assay was demonstrated using leukoagglutinating and erythroagglutinating lectins from the seeds of Phaseolus vulgaris and Maackia amurensis.