c-ets-1 and c-ets-2 are 2 proto-oncogenes known to be possibly involved in some human myelomonocytic leukemias. However, very few studies concern c-ets-1 and c-ets-2 RNA expression in human hematologic malignancies. We have studied 18 leukemic patients, and 10 cell lines for their ets RNA contents. c-ets-1 was strongly expressed in 5 and c-ets-2 in 8 of the 18 patients. All the cell lines expressed both c-ets-1 and c-ets-2 RNAs. This expression was highly variable from one patient to another, and from one cell line to another, regardless of the cellular leukemia subtype. The variability of this expression in patients may reflect differences in the proliferative potential of leukemic cells.