The influence of prostaglandins E2 and F2 alpha on passage pressure across the uterotubal junction (UTJ) and isthmus were studied in rats that were either in the pro-oestrus, oestrus, metoestrus or dioestrus phases. Effects of these prostaglandins were also investigated in rats that had been either ovariectomized and treated with oestradiol or medroxiprogesterone acetate, or only ovariectomized. In each rat, the left UTJ was surgically resected and the isthmus anastomosed to the uterine horn, whereas the right UTJ was left untouched. The passage pressures across the left isthmus and the right UTJ were measured before and after prostaglandin treatment. The pressures obtained in the UTJ in the oestrus phase and oestrogen-treated ovariectomized animals were lower than those registered in the remaining groups. Prostaglandin E2 decreased the pressures when compared with pre-treatment measures in all groups. Significantly higher pressures were registered across the UTJ in prostaglandin F2 alpha than in E2 treatment, with these higher pressures being similar to pre-treatment pressures. Both hormonal changes throughout the oestrous cycle and prostaglandin E2 treatment had a similar influence on the passage pressure across the isthmus, as that described for UTJ, but with lower values. The results indicate that prostaglandin E2 decreases the passage pressure across both UTJ and isthmus and can have an influence on the regulation of transport across these 2 areas.