Prostaglandins are bioactive lipids and important mediators of uterine relaxation as well as contraction during pregnancy and labour. E series prostaglandins may directly contract or relax myometrium in a dose-dependent manner, with the relaxatory effects mediated through the prostanoid receptors EP2 and EP4. The aim of this study was to evaluate the pharmacological effects of prostaglandin analogues on isolated pregnant rat uterine contractility, at 10- 15 to 10- 9 M concentrations. Uterine strips from rats at 19 days of gestation were set up in organ baths at 37 °C, bathed in Krebs buffer and gassed with 95% O2/5% CO2. Spontaneous contractions were recorded via a force transducer. Concentration ranges of 10- 15-10- 9 M of PGE2, PGF2α and a range of prostaglandin analogues were applied non-cumulatively to the tissues. Spontaneous contractions were recorded for 12 min post dose. Amplitude, frequency, baseline tone and percent contractility over 10 min periods were analysed. PGE2, butaprost, 9-keto fluprostenol, 11-keto fluprostenol, 9-keto fluprostenol isopropyl ester, AL8810 and 15(S)-15-methyl PGE2 all caused a decrease in percent contractility (P < 0.05). These agents, plus Δ12PGJ2 and 9-deoxy-9-methylene-16,16-dimethyl PGE2, also decreased frequency of contraction (P < 0.05). Only PGE2, PGF2α and 11-keto fluprostenol decreased baseline tone (P < 0.05). The lower concentrations of prostaglandins used here mediated inhibition of spontaneous contractility of pregnant rat myometrium. Use of selective agonists suggested that the prostanoid receptors EP2 and DP2 are responsible for this relaxatory effect.