The sex pheromone components of two species of Leucania that occur sympatrically in western Canada were identified in abdomen-tip extracts from calling female moths. (Z)-11-hexadecenyl acetate was the main component and (Z)-9-tetradecenyl acetate the second component in both species. The third component necessary for specific attractancy was (Z)-11-hexadecenyl aldehyde for L. anteoclara and (Z)-11-hexadecenyl alcohol for L. commoides. The third component for each species was an attractant inhibitor when added as a fourth component to the attractant blend for the reciprocal species. The most effective synthetic blend for the attraction of males in the field was Z9–14:Ac/Z11–16:Ac/Z11–16:Ald in a ratio of 1:10:4 for L. anteoclara and Z9–14:Ac/Z11–16:Ac/Z11–16:OH in a ratio of 5:4:1 for L. commoides.