Fermented aqueous suspension of whole-egg powder is attractive to Hippelates collusor (Townsend) (Diptera: Chloropidae) eye gnats and has been used for trapping eye gnats. Distillate of the fermented aqueous suspension was separated into water- and ether-soluble fractions by ether extraction. The 2 fractions were less attractive when tested individually. However, when these 2 fractions were combined and evaluated in an olfactometer against eye gnats in the field, the combination showed a significant increase in attractancy over the combined attractancies when evaluated separately. From the ethersoluble fraction, 10 carboxylic acids, n -butyric, iso -valeric, iso -caproic, myristic, palmitic, palmitoleic, stearic, oleic, linoleic, and linolenic, were isolated and identified as their esters with gas-liquid chromatography. Among these 10 acids, oleic and linoleic each enhanced the attractiveness of the water-soluble fraction; n -butyric, iso -valeric, and iso -caproic acids decreased the attractiveness of the water-soluble fraction; while myristic, palmitic, palmitoleic, stearic, and linolenic acids did not significantly influence the attractiveness of the water-soluble fraction.