The migrations of the sex myoblasts in Caenorhabditis elegans hermaphrodites involve two guidance mechanism: a gonad-dependent attraction that confers precise positioning of the sex myoblasts and a gonad-independent mechanism that is sufficient for coarse positioning in the absence of the gonad (Thomas et al., 1990). Here we show that mutations in unc-53, unc-71, and unc-73 disrupt sex myoblast positioning in the absence of the gonad, while they do not affect positioning in the presence of the gonad. Thus, mutations in these genes appear to compromise the gonad-independent mechanism without affecting motility or the gonad-dependent attraction. Mutations in sem-5 confer dramatic sex myoblast positioning defects in double mutant combinations with unc-53, unc-71, or unc-73 mutations, even in the presence of the gonad. This suggests that sem-5 is required for the gonad-dependent attractive mechanism. Mutations in let-60 ras and let-341 also confer sex myoblast migration defects in an unc-53 background, implicating these genes in gonad-dependent positioning as well.