Historically there has been some controversy over possible detrimental effects of exogenous prostaglandin F? ? ? (PGF? ?) administration on the function of the subsequent corpus luteum (CL). In the light of recent evidence that early luteal phase progesterone is essential for embryonic development (Mann et al., 1996) combined with the clinical use of PGF2? analogues in herd fertility management, an urgent need has arisen for this matter to be clarified. This abstract presents work designed to investigate whether two of the commercially available PGF? ? analogues used in veterinary therapy have any detrimental effect on corpus luteum function.