The metabolites of prostacyclin (PGI2) and thromboxane A2 (TXA2), 6-keto-PGF1α and TXB2, of maternal plasma, umbilical vessels and placental tissue in patients with pregnancy-induced hypertension (PIH) and essential hypertension complicated by pregnancy were measured and the results compared with those in patients with normal pregnancy. The 6-keto-PGF1α contents of maternal plasma, umbilical vessels and placental tissue in patients with PIH were significantly lower than those in patients with normal pregnancy, but the TXB2 contents revealed no significant difference between the groups. The role of the two prostanoids in the pathogenesis of PIH is discussed.