Observation of the oviposition behavior of cotton bollworm demonstrated the existence of substances that can act as oviposition deterrents. The scales, abdomens and tarsi of the moths, the most likely carrier, were extracted for the substances. An acetone extract exhibiting an oviposition deterrent effect was analyzed using gas chromatography and combined gas chromatography-massspectroscopy. Three components, 4-methyl-4-hydroxyl-pentanone-2, hexadecanoic acid and (Z)-9-octadecenoic acid, were identified, being present in the ratio 1:2:2. Experiments with synthetic mixtures indicated that a mixture of equal amounts of the two organic acids exhibited similar repellent and deterrent activity to a synthetic mixture of all three components. It is concluded that the natural oviposition-deterring pheromone is a mixture of hexadecanoic acid and (Z)-9-octadecenoic acid.