The male sex pheromone of the cockroachNauphoeta cinerea was isolated from adult sternal glands and identified by gas chromatography-mass spectrometry. This pheromone, which attracts females from a distance, is a multicomponent blend. It is composed principally of three compounds: 3-hydroxy-2-butanone (acetoin), 2-methylthiazolidine, and 4-ethyl-2-meth-oxyphenol. A mixture of synthetic compounds in a ratio of 4∶4∶1 (2700 ng) elicits maximal response and short latency of response by receptive females, similar to that induced by male sternal gland extracts. Tested separately, each compound induces a positive response, but the moving times spent by females are generally longer than with the mixture or extracts. These three volatile compounds also are found in small amounts (about 1/40 of sternal glands) in tergal gland secretions licked by females. Acetoin also is found in the sternal and tergal glands of two closely related speciesLeucophaea maderae andHenschoutedenia flexivitta. The biological relationship of each compound and pheromone blend to behavioral response is discussed.