A specific syndrome of prolonged gestation in sheep in South West Africa was studied and eventually reproduced by artificial feeding of the shrub, S. tuberculata var. tomentosa. lt was determined that the main period of insult occurred during the last 50 days of pregnancy. The trend of both progesterone and cortisol levels resembled those of normal ewes except for a considerable delay during this 50-day period. Apart from the abnormal length of gestation and concomitant features such as retarded udder development, no signs of toxicosis were manifested by the ewes. The most significant features in the postmature lambs were progressive hypophysial, adrenal and thymic atrophy; hypertrophy of the female genitalia, polyfollicularity of the ovaries and Leydig cell hypoplasia; long haircoat, erupted incisors and pigmentation especially of the kidneys and lymph nodes, but no abnormal a natomical features were found. ln rats, rations containing the shrub prolonged both gestation and the dioestrous phase of the oestrous cycle. The active ingredient of the plant is not an oestrogenic or a nti-oestrogenic substance. It was successfully extracted with alcoholic compounds.