†Division of Clinical and Experimental Endocrinology, University Women's Hospital, 34 Göttingen, and ‡Section of Biology of Reproduction, Department of Animal Science, 34 Göttingen, Federal Republic of Germany (Received 4 September 1975) To obtain information on the pituitary-gonadal system during sexual maturation in the pig, we have determined plasma luteinizing hormone (LH) and gonadal steroid levels in foetal, neonatal and pubertal animals of both sexes. Blood was collected from 45 male and 34 female miniature pig (Göttingen strain) foetuses between days 61 and 110 of foetal life (by cardiac puncture or from umbilical vessels). The piglets were removed 5–8 min after initiation of halothane anaesthesia in the sow. Blood (2–5 ml) was taken once by venipuncture of the jugular vessels from 79 male and 72 female unanaesthetized animals, 2 h (only females) to 12 weeks after birth. Plasma LH and progesterone were measured by radioimmunoassay (Pomerantz, Ellendorff, Elsaesser, König & Smidt,