In a genetically conditioned form of prolonged gestation in cattle, the postmature calves suffer from adrenal insufficiency (Holm, Parker & Galligan, 1961). Conversely, foetuses of habitually aborting Angora goats show adrenal hyperplasia (van Rensburg, 1965). The present work was undertaken with the aim of investigating the possibility that adrenocortical hormones may influence the duration of gestation in ruminants. Laparotomy was performed in Merino sheep in pentobarbitone anaesthesia by a midventral approach. In seven sheep a single uterine and amnio-chorion incision was made over the dorsal lumbar area of the foetus and each adrenal was exposed extraperitoneally. Curved forceps were applied to the adrenal vessels and left in situ after ablation of the gland until most of the lumbar musculature had been sutured. Foetal membranes were sutured simultaneously with the uterine incision. When portions of adrenal glands were removed, the amount was estimated by studying the morphology of the resected portion