The leaf beetle Diorhabda elongata Brullé (Coleoptera: Chrysomelidae) has been introduced as a biological control agent for saltcedars, Tamarix spp., an exotic, invasive weedy tree in the western United State. Gas chromatographic (GC) analysis of volatiles collected from feeding male or female beetles, or saltcedar foliage alone, showed two components produced almost exclusively by males. These compounds elicited responses from antennae of male and female beetles in GC-electroantennographic detection (EAD) analyses. The compounds were identified as (2E,4Z)-2,4-heptadienal (1) and (2E,4Z)-2,4-heptadien-1-ol (2) by GC-mass spectrometry (MS), and confirmed with authentic standards. The two compounds were also detected at trace levels from feeding females and foliage controls, but the amounts from feeding males were 8-40 times higher, typically 55-125 ng per day per male. The amounts of 1 and 2 in collections from females did not differ significantly from amounts collected from control foliage. In field trials, 2 as a single component was as attractive as a 1:1 blend of 1 and 2. Compound 1 as a single component was more attractive than controls, but much less attractive than 2 or the blend. Males and females were attracted in about equal numbers, indicating that this is an aggregation pheromone.