Two neurotransmitters, ACh and ATP, initiate nerve-mediated contractions in detrusor smooth muscle from guinea pig. In human detrusor from stable bladders ACh alone is the excitatory transmitter. However with human detrusor from unstable bladders ATP emerges as an additional transmitter and there is speculation that this may contribute to the pathology (Bayliss et al 1999). We are interested in the reasons why ATP has this action in human detrusor and one hypothesis is that nerve-mediated ATP release is enhanced. To this end we have evaluated the use of an amperometric ATP sensor in guinea pig detrusor smooth muscle. Detrusor strips were obtained from humanely killed guinea-pigs. Preparations were superfused at 37°C in a modified (glycerol 2mM) HCO₃^–/C0₂ Tyrodes solution (pH 7.3). An ATP sensitive sensor was calibrated in 10μM ATP solution and then placed on the muscle strip parallel to a null sensor. Contractions were elicited either by electrical field stimulation (EFS) or by agonists (carbachol 0.3μM or KCl 120mM). Raising the frequency of EFS in the range 2-12 Hz generated increasing sensor responses (n=4). These responses were completely abolished by the neurotoxin TTX (1 μM). To quantify ATP release, the signals were integrated over five seconds, following the end of the stimulation. At 2 Hz and 12 Hz ATP release was over the range 0.14-0.54 μmol.l^-1.s^-1.mg wet weight ^-1 and 0.21-7.87 μmol.l^-1.s^-1.mg wet weight^-1 respectively. A fraction of the ATP release with EFS may result from muscle contraction itself. This was assessed by contracting the preparation with carbachol and KCl, to elicit contractures of similar magnitude to that generated by 2-4 Hz EFS. Signals were generated by the ATP sensor that, except in one case, represented 10-30% of the signal produced by EFS. When the sensor was away from the muscle, EFS and KCl produced no response, although carbachol generated a small signal. We have demonstrated that it is possible to record ATP release from detrusor preparations and that a fraction of this can be attributed to a nerve mediated response. This method offers a sensitive and dynamic technique to investigate the role of ATP in regulating detrusor contractions.