Heritability of variation in male pheromone response by pink bollworm moths,Pectinophora gossypiella (Saunders), was examined using a still-air, wing-fanning bioassay. Heritability (±SE) of overall responsiveness, as measured by the mean duration of wing fanning to the blend of pheromone components produced by females [44∶56 ratio of (Z, E)- to (Z, Z)-7,11-hexadecadienyl acetate], was 0.385 ± 0.095. Heritabilities of wingfanning duration to blends with 25 and 65%Z, E isomer were 0.377 ± 0.113 and -0.145 ± 0.103, respectively. These findings indicate an asymmetry in the genetic component of variation in response to pheromone blends with high and low proportions of theZ, E isomer. An index of response specificity for individual males was developed based on the response to an off-blend (either 25 or 65%Z, E isomer) relative to the response to the 44%Z, E blend. Heritabilities of response specificity were 0.117 ± 0.059 and -0.043 ± 0.067 for the 25 and 65%Z, E blends, respectively.