Adenosine 5'-triphosphate (ATP) is known to play a significant role as a neurotransmitter in smooth muscle. There is evidence to show that ATP can cause bladder contractions and may also be involved in the processing of sensory information in the urinary bladder. These effects are likely to be mediated by P2X receptors, namely P2X(1) and P2X(3), respectively. This study set out to investigate their distribution in rat and human urinary bladders. P2X(1) receptor immunoreactivity was found on detrusor muscle fibres and P2X(3) receptor immunoreactivity was found in the urothelium of both species. This is the first demonstration of a non-neuronal localisation for P2X(3) receptors. No clear evidence was found for the presence of P2X(3) receptors on calcitonin gene-related peptide-containing sensory nerves and therefore P2X(3) receptors may not have a direct role in the mediation of sensory responses to ATP in the urinary bladder.