The olfactory responses of red flour beetles,Tribolium castaneum (Herbst), to methyl and ethyl ester of C14-C18 fatty acid prepared from tallow were studied. Methyl octadecanoate and ethyl octadecanoate discouraged aggregation of beetle adults. Ethyl 9.12-octadecadienoate acted as a repellent. Methyl pentadecanoate and ethyl tetradecanoate induced copulation at the level of 5 × 10(2) and 2 × 10(3) μg, respectively. The maximum response was observed at the level of 5 × 10(2) μg of the same compounds, and these compounds appear to stimulate males only.