Estrogen receptors (ER) and androgen receptors (AR) were determined in a series of 23 leukemia or lymphoma cell lines including 8 T-cell lines, 12 B-cell lines, and 3 non lymphoid cell lines. The phenotypic characterization of these cells by currently available immunological markers provides an estimate of their stage of differentiation. The result indicate that none of the investigated cell lines bear simultaneously ER and AR. Four were found to bear ER: U266, RPMI 8226, HL60, IARC/310/LT2, and four to express AR: RAJI, IARC/301/LTI, U937, REH6. The presence of cytosolic receptors was always associated with that of nuclear receptors. The expression of either ER or AR is restricted to discrete maturation stages of different haemopoietic cell lineages. Thus AR were found among the most immature lines of the T, B or monocytic lineage but they could be detected neither in the promyelocytic line HL60, nor in the pluripotential K562. The present results are in keeping with the demonstration of AR in some leukaemic blasts or in non Hodgkin's lymphomas. In contrast with AR, ER are present in two myeloma cell lines, in the promyelocytic cell line, HL60 and in a T-cell line bearing the phenotype of mature suppressor/cytotoxic T cells.