1. We examined the effects of two novel PGE1 analogs, SC-29169 and SC-31391, on bladder muscle isolated preparations from guinea pig and man, in comparison with some naturally-occurring prostanoids and misoprostol. 2. In the guinea pig detrusor muscle, both prostaglandin analogs enhanced twitch responses elicited by field stimulation in the following order of potency: SC-31391 greater than SC-29169 greater than PGF2 alpha greater than or equal to PGE2, while a well-defined contractile effect was elicited only by SC-31391. 3. In the human detrusor muscle, nerve-mediated responses were not modified by prostaglandin analogs, as well as by PGF2 alpha or PGE2, while a contractile effect was observed with the same compounds: PGF2 alpha = SC-31391 greater than SC-29169 = PGE2 = PGE1. 4. The selective EP1-agonist, misoprostol did not induce any effect, in both guinea pig and human bladder. 5. These data suggest that the effect of prostaglandins in the bladder muscle differs according to the animal species and that, in the human detrusor muscle, SC-31391 and SC-29169 probably stimulate FP receptors.