A nonvolatile, heat-stable contact pheromone, which aids males in identifying conspecific females, is present in Culiseta inornata. The pheromone is active for well over a week after a female dies, and it is soluble in, or destroyed by, diethyl ether, chloroform-methanol (2: 1), ethyl acetate, acetone, and water plus detergent. Activity is not affected by hexane, benzene, chloroform, or methanol. Bromine vapors destroy pheromone activity, and storage of female material in a phenolic atmosphere preserves activity for over a year. The phenomenon of heterogeneous summation may characterize the interaction of the contact pheromone and certain leg-associated tactile stimuli.