Male-female courtship interactions inDrosophila melanogaster are mediated in part by chemical cues. A comparison of the courtship behaviors of normal and genetically olfaction-deficient (olfD) flies lends strong support to this hypothesis and leads to the following inferences regarding the importance of chemical interchange during courtship. Virgin females respond to male courtship by slowing and finally stopping their movements, which appears to enhance the probability of copulation; (olfD) females are defective in this stopping response and in their receptivity to mating. Males can be stimulated to court by airborne cues from virgin females which are effective over a distance of ca. 5 mm. By comparison, the chemical courtship-stimulating cues from immature flies have little airborne efficacy; immature males appear to stimulate courtship only by contact chemoreception. The genetic upset or removal from courtship interactions of olfactory, visual, and auditory cues (thus leaving contact chemoreception as the probable major means of male-female interaction) results in virtual behavioral sterility.