The proteins encoded by the myc proto-oncogene family are involved in cell proliferation, apoptosis, differentiation, and neoplasia. Myc acts through dimerization with Max to bind DNA and activate transcription. Homologs of the myc and max genes were cloned from the fruit fly Drosophila melanogaster and their protein products (dMyc and dMax) were shown to heterodimerize, recognize the same DNA sequence as their vertebrate homologs, and activate transcription. The dMyc protein is likely encoded by the Drosophila gene diminutive (dm), a mutation in which results in small body size and female sterility caused by degeneration of the ovaries. These findings indicate a potential role for Myc in germ cell development and set the stage for genetic analysis of Myc and Max.