We have isolated overlapping genomic clones that contain a single-copy myosin heavy-chain gene of Drosophila melanogaster. By the criteria of hybridization under nonstringent conditions, this is the only myosin heavy-chain gene of the fly. The gene is localized to the chromosomal region 36B. The transcriptional unit has a length of about 19 kb and contains at least nine introns. There are three mature mRNA species expressed from the gene, with molecular lengths of 7.2 kb, 8.0 kb and 8.6 kb. The former two are expressed abundantly during those stages of development when larval muscle proteins are being synthesized; the latter two are expressed when the principal muscle proteins of the adult are made. The three transcripts differ primarily in their respective patterns of splicing at the 3' ends.