An additional genetic locus in Caenorhabditis elegans, unc-116, was identified in a screen for mutations resulting in defective locomotion. unc-116 was cloned by use of a transposon insertion mutant and the physical and genetic map of the genome. The cDNA sequence predicts an 815-amino acid protein. Based upon sequence comparison and secondary structure predictions, unc-116 encodes all three domains of the kinesin heavy chain: the motor, stalk, and tail. While the motor and tail domains have a high degree of identity to the equivalent domains of cloned kinesin heavy chains, the rodII domain of the stalk is significantly shorter than those previously reported and is not predicted to form a coiled-coil alpha-helix. Analysis of mutational defects in two C. elegans genes encoding anterograde motor molecules, unc-116 and unc-104, should provide insight into the in vivo functions of these members of the kinesin heavy chain superfamily.