Three compounds have been identified as sex pheromone components produced by female fall webworm moths,Hyphantria cunea (Drury). These compounds are: (Z,Z)-9,12-octadecadienal (I), (Z,Z,Z)-9,12,15-octadecatrienal (II), and (Z,Z)-3,6-cis-9,10-epoxyheneicosadiene (III). The ratio of these compounds was approximately 5∶6∶13, respectively, in female tip extracts prepared from U.S.S.R, insects and approximately 1∶8∶21, respectively, in extracts from U.S. insects. The ratio in female effluvia trapped from U.S. insects was 1∶6∶27, respectively. Compound III plus either I or II is effective in eliciting upwind flight in a wind tunnel. Compounds I, II, and III are also components of the sex pheromone system of the saltmarsh caterpillar moth,Estigmene acrea (Drury).