The effect of prostaglandin E 2/PGE 2/ and indomethacin on 3H-noradrenaline (3H-NA) release- and on contractions-evoked by field electrical stimulation (FES) was studied in vitro in oviductal isthmus of mature rabbits (untreated and treated with estradiol). FES evoked guanethidine-sensitive contractions and calcium-dependent tritium overflow, which reflected 3H-NA overflow. Markeed and concentration-dependent decrease of FES-evoked contractions by PGE 2 (0.1–100 nM) was observed in both groups of animals. The inhibitory effect of PGE 2 was more pronounced in estradiol treated animals (RC 50 1.5 nM, n=9) than in untreated animals (IC 50 18 nM, n=6). Indomethacin, 1 μM, induced a remarkably pronounced increase of FES-evoked contractions in estradiol treated (by 57.3 ± 6.3%, n=8), in comparison with untreated rabbits (21.4 ± 3.8%, n=7). The amount of FES-evoked release of tritium was significantly higher in untreated than in estradiol treated rabbits. PGE 2 decreased and indomethacin increased tritium-evoked release. The effects of PGE 2 and indoemethacin on tritium-evoked release showed no estradiol dependence. The competitive results of PGE 2 and indomethacin on both evoked contraction and 3H-NA release suggest that endogenous prostaglandin E 2 takes part in modulation of adrenergic mediated contraction and that estradiol enhanced the prostaglandin effect.