The possible role of PGs in hyoscine-resistant nerve mediated responses of the rat urinary bladder was investigated. Responses to electrical stimulation were inhibited by cinchocaine (30 micronmol/1) but were only partially inhibited by a high concentration of hyoscine (25 micronmol/1) or by the choline uptake inhibitors, hemicholinium-3 (500 micronmol/1) and troxypyrrolidinium (500 micronmol/1). Indomethacin (50 micronmol/1) produced partial blockade (30%) of responses to electrical stimulation without markedly affecting responses to acetylcholine and the degree of blockade was of a similar order in the presence of hyoscine or troxypyrrolidinium. PGE2 (0.028 -2.8 micronmol/1) or F2alpha (0.029 -2.9 micronmol/1) produced a slowly developing increase in tone and spontaneous activity. Responses to electrical stimulation were at most only slightly increased in the presence of either PG. However, the PGs always increased the responses to electrical stimulation after indomethacin, indomethacin plus hyoscine or indomethacin plus troxypyrrolidinium. Responses to acetylcholine in the presence of indomethacin were not increased by PGE2. It is concluded that PGE2 and F2alpha do not function is transmitters responsible for resistance to anti-muscarinic drugs in the bladder but may exert a modulating effect on nervous transmission.