We have examined the expression of three cellular oncogenes (c-Ki-ras, c-Ha-ras and c-myc) in different stages of murine erythroleukemias induced in ICFW mice by Friend viruses (F-MuLV and SFFV) in comparison to normal mice spleens and bone marrows, including erythropoietically-stimulated spleens from phenylhydrazine-treated mice. There is no evidence of c-Ki-ras RNA expression in any of the tissues tested. c-Ha-ras RNA was found at similar levels in erythroleukemic cells and normal erythroid cells. In contrast, increased levels of normal 2.3 Kb and short 1.8 Kb c-myc RNA transcripts were detected in both early preleukemic and late leukemic phases of the diseases, as compared to normal erythroid cells. Apparently, neither myc gene amplification nor myc gene rearrangement was observed in erythroleukemias. Our results suggest a possible involvement of c-myc gene either in erythroid cell differentiation or in an early proliferation step of the erythroleukemic process.