Lindane (gamma-Hexachlorocyclohexane) was orally given to pregnant Swiss female mice at various stages of pregnancy. During early pregnancy (1-4 days of gestation), the insecticide caused total absence of any implantation site, while given during mid pregnancy (6-12 days of gestation), lindane caused total resorption of fetuses. Lindane administration during late pregnancy (14-19 days of gestation) resulted in death of all pups either within 12 h (high-dosed group) or 5 days (low-dosed group) of parturition. Body weight of such pups were also highly reduced. When estrogen was given together with lindane at early pregnancy, implantation was normal, although subsequent fetal development was adversely affected. Progesterone, unlike estrogen, could not correct lindane-induced failure in implantation. On the other hand, when estrogen and progesterone were simultaneously given to lindane-fed mice during early pregnancy, both implantation and subsequent fetal development became comparable to normal mice. The insecticide besides being fetotoxic, thus appears to cause steroid hormone deficiency resulting in reproductive and developmental failure.