The 1,966-amino acid unc-54 myosin heavy chain sequence was determined from DNA sequence studies of the cloned gene. The gene is split by eight short introns, 48-561 base pairs long, and appears to lack a "TATA" box at its promoter. The physical map of the gene was aligned with the genetic map by locating two point mutations and three internal deletions: 0.01 map units correspond to approximately 5 kilobases. Comparison of the unc-54 protein sequence with the sequence of a second myosin heavy chain from nematode, indicates that the globular head sequence S-1 is more highly conserved than the alpha-helical coiled-coil rod. Major sites of proteolysis in S-1 are associated with variable sequences that have the characteristics of surface loops. In both genes there is no correlation between the positions of introns and the major protein structural domains.