To determine whether Heliothis virescens and H. subflexa, two closely related sympatrically occurring species, differ in their antennal responses to conspecific and heterospecific pheromone compounds, we recorded electroantennogram (EAG) responses of male and female antennae of both species to eight different compounds loaded on filter paper dispensers. If antennal responses were found to differ in the two species, EAG-recordings from F₁ hybrids and backcrosses between these species could be used in developing an understanding of the genetic architecture of variation in olfactory signal perception. However, all compounds elicited EAG responses in all male antennae tested, and no quantitative differences in response were found between the two species, except for the response to 1 mg (Z)-11-hexadecenol (Z11–16:OH), which elicited larger EAG responses in H. subflexa than in H. virescens males. This difference is consistent with the idea that this pheromone component is less important in the biology of H. virescens. Female antennae of both species were less responsive to the major sex pheromone compound, (Z)-11-hexadecenal (Z11–16:Ald), than male antennae; 10 μg Z11–16:Ald, which elicited strong EAG responses in males, produced female EAGs similar to control puffs of air. However, higher doses of Z11–16:Ald elicited significant EAG responses in female antennae of both species. Female antennae of both species also responded to most other pheromone compounds, except Z11–16:OH. These results support the hypothesis that autodetection of sex pheromones occurs in females of both H. virescens and H. subflexa. Whether females behaviorally respond to any, or to combinations, of these compounds remains to be elucidated.