ATP contributes to nociceptive sensory processing by activating a family of ligand-gated ion channels, the P2X receptors. One of these, the P2X3 receptor, is highly localized on primary afferent neurons. In sensory neurons, P2X3 receptors function as homomeric (P2X3) and heteromeric (P2X2/3) channels. Exogenous application of ATP and related agonists excites peripheral and central nerves, and increases sensitivity to noxious stimuli. Specific targeting of P2X3 receptors by gene deletion and knockdown results in a hypoalgesic phenotype. In animal models of pain, pharmacological blockade of P2X3 receptors fully blocked specific types of chronic inflammatory and neuropathic pain. Peripheral nerve injury differentially alters functional expression of P2X3 receptors on small and large diameter primary afferent neurons. These data have delineated discrete roles for homomeric P2X3 and heteromeric P2X2/3 receptor activation in acute and chronic pain. Similar findings have also been generated from extensive research of the bladder urothelial-sensory neuron system. The urinary bladder is richly innervated by P2X3 receptor-containing neurons. Heteromeric P2X2/3 channels in the bladder contribute to both mechanosensitivity and nociceptive responses. Thus, both genetic and pharmacological approaches have provided converging evidence that activation of P2X3-containing channels is an important mediator of acute and persistent nociceptive signaling in the peripheral nervous system.