The California prionus (Prionus californicus Mots), is widely distributed in western North America from Baja Calif. to British Columbia and Alberta. This beetle is known to attack many plants including oak, pine, poplar, apple, apricot, and grape and it is a serious pest of hop in Idaho. It has been thought for many years that female P. californicus use a sex pheromone to attract males for mating. Olfactometer experiments were conducted to determine if male beetles respond to olfactory cues from female beetles or their volatiles placed on cotton dental wicks. Sixty-five (87%) of the 75 responding males moved to the olfactometer chamber containing the female beetle, this difference was statistically significant from the expected response of 50% under the null hypothesis (ƒÓ2 1,75 P < 0.001). Headspace volatiles collected from P. californicus adults were analyzed by GCMS for differences in volatile profiles between male and female beetles. Female°Vspecific compounds were tested in a y-tube olfactometer for activity against males.