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Secretion rates of ovarian steroids were measured in five ewes in which the left ovary was transplanted to the neck. Progesterone, 20-dihydroprogesterone, androstenedione, testosterone, oestrone and oestradiol-17β were measured in samples of ovarian venous blood collected twice weekly for six periods of 4–9 weeks. The secretion of progesterone (range < 2–804 µg./hr.) showed some cyclical variation in four collection periods with a minimum estimated cycle length of 20 days. 20-Dihydroprogesterone was present in quantities of about 1/50th of that of progesterone. The maximum secretion of oestradiol-17β (up to 250 ng./hr.) occurred at the same time as the minimum secretion of progesterone. The secretion of oestrone (0–88 ng./hr.), androstenedione (59–159 ng./hr.) and testosterone (20–90 ng./hr.) followed that of oestradiol-17β. In two animals there was a constant high secretion of progesterone throughout the collection periods, indicating the persistence of a corpus luteum. None of the ewes with transplanted ovaries showed behavioural oestrus regularly. These changes of ovarian function after transplantation to the neck could be explained by physical separation of the ovary and the uterus.

On seven occasions systemic administration of pregnant mare serum gonadotrophin (PMS, 750–1000 i.u.) was followed by a marked rise in the secretion rate of oestradiol-17β, androstenedione and testosterone. There was a progressive increase in the secretion of progesterone beginning about the 5th day after PMS in three experiments when the secretion was below 25 µg./hr. in the control samples.