The contractile response of guinea-pig urinary bladder to agonists following exposure to 3'-O'-(3(N-(4-azido-2- nitrophenyl)amino)propionyl) adenosine-5'-triphosphate (AA ATP) was investigated. Urinary bladders were obtained from male albino- guinea-pigs, and isolated strips were placed in a chamber at 37 degrees-C. After 1 hour of equilibrium the tissues were photoactivated in the presence of AA ATP. Response was elicited by addition of acetylcholine (51843), potassium-chloride (7447407), or adenosine-triphosphate (56655) (ATP) and by electrical stimulation. A dose response curve was obtained non cumulatively by progressive increases in agonist concentration. Neurogenic response was tested by exposure to the agonists, AA ATP and atropine (51558), or pretreatment with 6-hydroxydopamine (1199184). AA ATP antagonized the contractile response of guinea-pig urinary bladder strips to ATP, but produced no significant antagonism of the response of the bladder to acetylcholine or potassium-chloride. Response to ATP was also reduced when AA ATP was used without photoactivation. After removal of AA ATP and in the presence of atropine, the response to ATP was restored to central values, but the response to acetylcholine was nearly abolished. The frequency response curve of the urinary strips was not altered by AA ATP or photolyzed AA ATP, but combined treatment with atropine and AA ATP produced a marked inhibition of the neurogenic response of the bladder, and this effect was greater than with either agent alone. Effects of atropine and atropine plus AA ATP on the neurogenic bladder response from animals pretreated with 6-hydroxydopamine were significantly less than relative responses of the tissue from untreated animals. Under these conditions atropine alone was a more effective antagonist than was 6-hydroxydopamine and AA ATP treatment combined. Response of the bladder strip to electrical stimulation was not antagonized by AA ATP or atropine. The authors conclude that acetylcholine and a purine release from cholinergic and dopamine sensitive nerves, respectively, are involved in motor transmission in the guinea-pig urinary bladder.