Over the last decade, the c-myb gene and its protein product, Myb, have undergone extensive examination and manipulation in hemopoietic tissues. Although it is rarely disputed that, as a transcription factor, Myb regulates cell cycling, proliferation and differentiation, identification of genes directly controlled by Myb has been surprisingly difficult. More recently, genes with promoter regions that contain Myb recognition sequences have been identified, but a direct proliferative response to Myb via these 'target genes' has yet to be demonstrated. Mutagenesis studies have defined domains of the protein which influence its transcriptional activity and transforming potential; however how the molecule interacts with itself and with other cellular factors is only beginning to be understood. A broader examination of c-myb expression in normal and malignant tissues suggests an analogous role for Myb in proliferation, differentiation and transformation of non-hemopoietic tissues.