To better understand the heterogeneity of chronic B-cell leukemias we correlated morphological and immunological features by studying the peripheral blood from 80 patients with a panel of anti-immunoglobulin and fourteen monoclonal antibodies, which hitherto were studied separately or with respect to one single morphological entity only. Of these the surface immunoglobulins (sIg) and monoclonal antibodies (McAb) BA-1, BA-2, FMC7, OKM1, and anti-T65 allowed a fair distinction between five cytological subtypes: chronic lymphocytic (CLL), "lymphoplasmacytoid" (LPL), centrocytic (CL), prolymphocytic (PLL), and hairy cell leukemia (HCL). In that order the sIg showed a decreasing number of cases of mu +/- delta class and an increase of alpha or gamma positivity. The number of BA-1-positive cases was decreased in PLL and HCL. There was a decline of BA-2- and anti-T65-positive cases in the order mentioned, while this was accompanied by an increase of FMC7 and OKM1 positivity. A significant mutual exclusion between anti-T65 and FMC7 was observed and the same was true for FMC7 and BA-2. The antibodies FMC7 and OKM1, and anti-T65 and BA-2 were linked to each other. Also FMC7 positivity was related to sIg of the alpha and gamma classes. On the basis of this unique combination of markers a differentiation scheme of B lymphocytes is proposed, in which prolymphocytic leukemia and hairy cell leukemia seem to represent a maturation arrest at a more advanced stage than chronic lymphocytic or "lymphoplasmacytoid" leukemia.