Cholesterol side-chain cleavage of mitochondria, the key rate limiting step in steroid biosynthesis in ovarian tissues, was studied in female Swiss mice fed lindane (γ-hexachlorocyclohexane) at various doses and over varying periods. The insecticide adversely affected cholesterol side-chain cleavage of the ovary as judged by decreased conversion of this sterol to pregnenolone and subsequently to progesterone in a dose-dependent manner. The formation of pregnenolone was maximally inhibited (75% inhibition) at the highest intake of insecticide with simultaneous inhibition of its conversion to progesterone. At all doses, the rate of inhibition of pregnenolone formation was comparatively higher than its conversion to progesterone. The significant inhibition of cholesterol side-chain cleavage by lindane and resultant decrease in the rate of steroidogenesis in the ovary would account for the observed gonadal hormone deficiency and related reproductive disorders in the lindane-fed mice. © 1990.