The biosynthesis and metabolism of prostaglandin E2 was studied in cell-free homogenates of tissues from the uterus and foeto-placental unit using specific in vitro methods. The results show that the synthesis of prostaglandin E2 is greater in endometrial tissue from the secretory phase (53.07 +/- 39.05; ng/100 mg wet tissue/h) than from the proliferative phase of the uterine cycle. Furthermore, endometrial tissue forms more of this compound than myometrium (P less than 0.005). During early pregnancy, synthesis is decreased (25.10 +/- 16.62); at term, myometrium produces more prostaglandin E2 than decidua. During labour, however, decidual tissue accumulates more of this compound (52.73 +/- 18.04) than either myometrium (34.71 +/- 13.19) or cord (28.63 +/- 11.71). The catabolic enzymes are most active in the placenta and chorion, followed by the cord, myometrium, decidua and amnion, but the differences have only a slight effect on the amounts of prostaglandin E2 which remain at the end of the incubation. The results suggest a high turnover of prostaglandin E2 in the decidua, myometrium and cord.