Placental bed biopsies were obtained during caesarean section from normal, pre-eclamptic and hypertensive pregnancies. Of the 14 biopsies from normal pregnancies 13 showed normal vascular physiological changes in the decidua and in the myometrium. Biopsies from 24 pregnancies complicated by pre-eclampsia showed acute atherosis in 18 and physiological changes limited to the decidua in six; none had normal physiological changes. Biopsies from five hypertensive patients showed all three types of histological changes. The mean birthweight centile was lower in the group with atherosis than in the group with limited and the group with normal physiological changes.