The female-produced sex pheromone blend of the pandora moth, Coloradia pandora pandora Blake, a pest responsible for periodic defoliation of pine forests in the western United States, has been identified. The pheromone consisted of a mixture of E10,Z12-hexadecadienal, E10,Z12-hexadecadienyl acetate, and E10,E12-hexadecadienyl acetate. All three components were essential for optimal attraction. E10,Z12-Hexadecadienol, tentatively identified in trace amounts in pheromone gland extracts, elicited strong responses from male antennae in coupled gas chromatography – electroantennogram analyses but had no apparent effect as a pheromone component at physiologically relevant levels. Hexadecanal, octadecanal, and hexadecyl acetate also were identified in extracts of female pheromone glands but elicited no responses from male antennae, nor did they appear to be components of the attractant blend. In field trials, each trap baited with the optimized three-component blend of E10,Z12-hexadecadienal, E10,Z12-hexadecadienyl acetate, and E10,E12-hexadecadienyl acetate captured an average of more than 40 male moths per night.