rax-4 was identified in screens for genes that regulate outgrowth and pathfinding of male sensory ray neuron axons; the rax-4 mutation, specific for ray neurons, results in defects in dorsoventral axon growth cone migration and genetic analyses suggest that rax-4 functions in the unc-6/netrin - unc-40/DCC pathway to regulate this aspect of ray neuron development; the rax-4 mutation also affects at least two aspects of male copulatory behavior: response to hermaphrodite and ventral turning.