The effects of TPA (12-0-tetradecanoylphorbol-13-acetate) and RA (retinoic acid) were investigated on the cell lines HL60 (acute promyelocytic leukemia) and K562 (erythroleukemia) and on cells from patients with several kinds of leukemia. There were 14 cases of acute lymphocytic leukemia (ALL), 2 cases of chronic lymphocytic leukemia (CLL), 23 cases of acute myeloid leukemia (M1-M7), 5 cases of chronic myelocytic leukemia in blast crisis (CML-BC) and 2 mixed leukemias. In almost all of the cases examined, after TPA exposure cells from patients with proven myeloid leukemia became adherent to the substrate, while lymphoid leukemia cells remained in suspension, allowing the differentiation of lymphoid from myeloid blasts. The only exception was in one case of CLL, which had cells that became adherent with long filamental projections. In addition, increased phagocytosis following TPA exposure permitted characterization of M7 as this was the only myeloid leukemia negative for phagocytosis. Further discrimination between the subtypes of myeloid leukemia could be based on the increased lysozyme production seen after TPA in M4 and M5. Esterase positivity allowed the discrimination of M1 cells, which were negative before and after TPA treatment. In agreement with the results of other authors, TPA and RA led to independent ways of differentiation, granulocytic-like lineage and monocytic-like cells being favored by RA and TPA, respectively. The capacity of the same cell to differentiate into more than one lineage, depending on whether RA or TPA was used, was only seen in the present study with M3 cells.(ABSTRACT TRUNCATED AT 250 WORDS)