The few documented cases of natural hybridization in Drosophila species are reviewed. Evidence for introgression between D. pseudoobscura and D. persimilis and between two pairs of Hawaiian species, D. heteroneura and D. silvestris, and between D. setosimentum and D. ochrobasis, are discussed. Gene flow between D. heteroneura and D. silvestris appears to be unidirectional, based on morphological data. It is suggested that the dynamics of sexual selection plays an important role in permitting occasional hybridization in nature and that this allows limited introgression without destroying the genetic integrity of the species. Also, introgressive hybridization, induced by the dynamics of the sexual selection process, may play an important role in the origin of new genetic material in sympatric populations.