ATP is a putative inhibitory neurotransmitter responsible for inhibitory junction potentials at neuromuscular junctions (IJPs) in the intestine. This study tested the hypothesis that the purinergic P2Y₁ receptor subtype mediates the IJPs. IJPs were evoked by focal electrical stimulation in the myenteric plexus and recorded with "sharp" intracellular microelectrodes in the circular muscle coat. Stimulation evoked three categories of IJPs: (1) Purely purinergic IJPs were suppressed by the selective P2Y₁ purinergic receptor antagonist, MRS2179. Purely purinergic IJPs comprised 26% of the IJPs. (2) Partially purinergic IJPs (72% of the IJPs) consisted of a component that was abolished by MRS2179 and a second unaffected component. The MRS2179-insensitive component was suppressed or abolished by inhibition of formation of nitric oxide by L-NAME in some, but not all IJPs. An unidentified neurotransmitter, different from nitric oxide, mediated the second component in these cases. (3) Non-purinergic IJPs were a small third category (4%) of IJPs, which were abolished by L-Name and unaffected by MRS2179. Exogenous application of ATP evoked IJP-like hyperpolarizing responses, which were blocked by MRS2179. Application of apamin, which suppresse opening of small conductance Ca²⁺-operated K⁺ channels in the muscle, decreased the amplitude of the purinergic IJPs and the amplitude of IJP-like responses to ATP. The results support ATP as a neurotransmitter for IJPs in the intestine and are consistent with the hypothesis that the P2Y₁ purinergic receptor subtype mediates the action of ATP.