The activities of glucose-6-phosphate dehydrogenase, Δ5-3β-hydroxysteroid dehydrogenase and succinic dehydrogenase were studied histochemically in the ovary of normal and malonate treated hens. Following malonate treatment, glucose-6-phosphate dehydrogenase and Δ5-3β-hydroxysteroid dehydrogenase showed increased activities while succinic dehydrogenase activity was diminished significantly. The significance of the above changes is discussed. The ascorbic acid and cholesterol contents of the ovary were determined to get additional information about steroidogenesis in the gland under such treatment.