In chronic myeloid leukemia (CML), a chromosome translocation has fused the bcr gene to the c-abl oncogene, such that a chimeric bcr-abl polypeptide can be made. To explore the biological properties of bcr-abl and compare them with those of the Abelson virus (AMuLV) transforming gene (gag-v-abl), we have used either a synthetic bcr-v-abl gene that mimics the translocation product or, in some experiments, a bcr-c-abl cDNA. A new retroviral vector was used to introduce the genes into the factor-dependent myeloid line FDC-P1. Both bcr-abl and v-abl efficiently rendered the myeloid cells factor independent and tumorigenic. Their fully autonomous growth may be due to the myeloid growth factor interleukin-3 (IL-3) made in small amounts by the infected cells. Hence autocrine factor production may feature in CML development and Abelson virus transformation.