A laboratory method has been devised for testing the attractancy of vapors to adultOryzaephilus surinamensis (L.). Of four solvent extracts prepared from pods of the carob tree [Ceratonia siliqua (L.)], all attractedO. surinamensis, but the least polar extract was the most active. Subdivision of extracts yielded a series of fractions, the most attractive of which contained a mixture of triglycerides with three or more double bonds per molecule. Twelve authentic triglycerides, either synthesized or purchased, elicited responses ranging from high to very low attractancy in a way which appeared to be related to the number, position, and geometrical shape of the double bonds in the molecules. By studying the response of the insects to five glyceride acids, three aldehydes, and three volatile fatty acids, it has been shown that it may be possible to explain the attractancy attributed to the triglycerides, which are involatile, in terms of the response to their volatile breakdown products.