We have isolated phage clones containing the D. melanogaster sequence homologous to the v-abl oncogene, and two types of phage clones containing sequences homologous to the v-src probe. The D. melanogaster abl clone (lambda Dabl1) and one of the src clones (lambda Dsrc1) hybridize with both v-abl and v-src probes, and both map in situ to the same chromosomal position, 73B, on chromosome arm 3L. The second D. melanogaster src clone (lambda Dsrc2) does not react with the v-abl probe and hybridizes in situ to chromosomal position 64B. The hybridization pattern suggests that the src and abl cellular oncogenes have evolved from a common prototype sequence. The homologous sequences in D. melanogaster exhibit hybridization to regions in the vertebrate v-abl and v-src that are important for kinase activity and transforming potential of the viral gene products.