The expression of a novel B-cell-associated carbohydrate epitope (1D8) was studied by means of flow cytometry in 153 well defined cases of leukemias and lymphomas and 19 cases of lymphadenopathy used as controls. The 1D8 epitope was detected preferentially in proliferations of mature B-lymphocytes (11/15 CD20+ acute lymphoblastic leukemia (ALL), 14/16 chronic lymphocytic leukemia (CLL), 4/7 mantle cell non-Hodgkins lymphoma (NHL), 3/8 follicle cell NHL. However its expression did not appear lineage- or differentiation stage-restricted. Intensive expression on in vivo and in vitro-activated lymphocytes as well as in some high grade malignancies indicated a relationship to the functional state of cells. Bearing in mind the enhanced detection of 1D8 upon desialylation, the epitope might be involved in the regulation of adhesion/migration potential of normal leukocytes and their malignant counterparts.