D. neorepleta wild type [female] [female] have been crossed with white-eyed D. repleta [male] [male] producing wild-type F1 offspring: sterile d d with narrow testes, and variable [female] [female], some of them suggesting intersexuality. F1 [female] [female] backcrossed to white repleta [male] [male] give white and wild offspring but a deficiency from the expected proportion of white [female] [female], and of the few white [female] [female] observed at least some were intersexes. The wild-type dd from the backcross resemble F1 [male] [male] in being sterile but some of the wild-type [female] [female] were fertile and were backcrossed to white repleta [male] [male] through many successive generations. Crossover tests indicate that the locus of the narrow-testis gene lies between white and singed and very near white. Some wild-type [female] [female] from the backcross when mated to white repleta [male] [male] gave the 4 types of offspring in approx. equal nos., others gave a marked deficiency of white daughters. Backcrosses of 1/2 the wild-type daughters of the latter gave equal distributions of type, the other 1/2 gave very few white [female] [female] (possibly crossovers) and a number of white intersexes of extreme type. Pre-imaginal mortality may account for the relative infrequency of these intersexes. It is concluded that D. neorepleta carries an autosomal gene which when present in a single dose makes her eggs [male] in potentiality. This is only partially overcome by 2 repleta X''s and [male]-like intersexes result. If one of the X''s is a neorepleta X, however, normal [female] [female] are produced. 2 neorepleta X''s cause normal [female] [female], but some F1 hybrids having one repleta X and one neorepleta X develop into [female] [female] with [male]-like anal plates. Presumably the, [male]-determining action of the autosomal gene and the [female]-determining action of the X are both stronger in neorepleta.