Previous studies have shown that both an intact hypothalamic-pituitary-adrenal axis and prostaglandin E 2 (PGE 2 ) are involved in the timing of parturition in sheep. PGE 2 is known to be synthesised by the placenta but has also been found in the foetal brain and pituitary. We propose that the enzymes necessary for production of PGE 2 are found in the ovine foetal pituitary and may be able to exert an autocrine and/or paracrine influence on corticotropes, resulting in an increased secretion of immunoreactive adrenocorticotrophin (irACTH). Pituitary tissues from foetal sheep, of gestational ages 119-126 days, were examined by immunohistochemistry. Primary antibodies for prostaglandin H synthase-1 and -2 (PGHS-1 and PGHS-2), microsomal prostaglandin endoperoxide synthase (mPGES) and irACTH were used to probe expressed proteins and Alexa-Fluor red-and green-fluorescent secondary antibodies were used to visualise the bound primary antibody. Staining for PGHS-1, PGHS-2 and mPGES was found throughout the foetal anterior pituitary. PGHS-1 and mPGES were widely distributed, including but not restricted to corticotropes. PGHS-2 was less widely distributed but occasionally was found in cells adjacent to corticotropes. The results indicate that locally produced prostaglandins may have an influence on the secretion of ACTH, independent of placental PGE 2 .