The effects of prostaglandin E2 (PGE2) on the contractile activity of thyroidectomized and thyroxine-treated albino rats were studied in vitro. Thyroidectomy totally inhibited the contractile response of the vas deferens to PGE2. Thyroxine treatment, on the other hand, significantly (P < .001) potentiated the response of vasa deferentia to PGE2, when compared to controls. It is suggested that thyroid hormones play a role in the contractile response of the vas deferens to PGE2.