Concanavalin A capping was studied in immunoglobulin-secreting hybridomas derived from fusion of mouse myeloma NSO cells with mouse spleen lymphocytes. The cells of the parental populations differed significantly in capping ability (low in myeloma cells and high in the lymphocytes). Among the hybridoma cells tested, several clones showed low capping, similar to that of the myeloma cells, some showed a good degree of capping, similar to that of the lymphocytes and other clones expressed an intermediate capping response. Capping was significantly increased in hybridoma clones of intermediate capping ability following in vivo intraperitoneal growth. A possible relationship of the variation in capping response to cell motility and to metastatic capacity is pointed out.