The effcets of adenosine 5`-triphosphate(ATP) were investigated on the uterine smooth muscle motility in the pig. The results were summarized as follows: 1. The effects of the porcine uterine smooth muscle and the contractile responses increased between the concentration of ATP 10(-5) and 10(-3)M with a dose-dependent manner. 2. The contractile response induced by ATP(10(-4) M) was not blocked by pretreatment with cholinergic receptor blocker, atropine (10(-6) M). 3. The contractile response induced by ATP (10(-4) M) was not blocked by pretreatment with α-adrenergic receptor blocker, phentolamine (10(-6) M) and β-adrenergic blocker, propranolol (10(-6) M). 4. The contractile response induced by ATP(10(-4) M) was not appeared in Ca(++)-free medium. As the concentration of Ca++ in Ca(++)-free medium was increased, the contractile response induced by ATP (10(-4) M) was enhenced but was completely inhibited by pretreatment with Ca(++)-channel blocker, papaverine(10(-6) M) or verapami1(10(-6) M). From these results, it was conclued that the effects of ATP were the contraction mediated by purinergic receptor in uterine smooth muscle of pig.