Fetal parts of placentomes from two cows with normal parturition, two cows with flumethasone induced parturition and two cows with preterm caesarian section were incubated in vitro with 'Handrostenedione (AD), 'H-dehydroepiandrosterone (DHA) or 'H-epitestosterone (ET).After 2.5 hours the samples were extracted, the steroids separated using column and thin layer chromatography and quantitated by liquid scintillation counting.AD was metabolized into oestrogens to the extent of 55 %, DHA 45 % and ET only 14 YO.In a second experiment 1 g of steroid (DHA-sulphate, DHA or AD) were each infused into two late pregnant cows. Blood samples were collected and the concentrations of DHA-sulphate, DHA, AD, ET, testosterone, oestrone, oestradiol-17P and conjugated oestrogens were measured by radioimmunoassay. During infusion, the levels of the infused androgens rose to 150-1,000 ng/ml, whereas the oestrogen concentration increased only twofold.From these results we conclude that the bovine placenta does not need maternal androgens for oestrogen biosynthesis.