OBJECTIVE The aim of our study of the pig was to investigate the responses of smooth muscle of the bladder and the urethral sphincter to preganglionic parasympathetic stimulation, and to assess the effect on the lower urinary tract of IV administration of alpha,beta-methylene-ATP. METHODS In seven anaesthetised female pigs, the responses to repeated 20 s pelvic nerve stimulations before and after IV administration of 0.02 mg/kg alpha-beta-methylene-ATP, and the responses to the drug itself, were recorded in the bladder and the urethra separately. RESULTS In the urethral high-pressure zone, pre-stimulation pressure was a mean of 61+/-11 cmH2O. During pelvic nerve stimulation, urethral pressure declined by 48+/-9 cmH2O, while the bladder pressure increased to 30+/-18 cmH2O. The rate of pressure changes during the first 3 s of stimulation (initiation of voiding) was larger in the urethra than in the bladder (urethral pressure decrease: 13.0+/-3.1 cmH2O/s, bladder pressure increase: 3.2+/-2.5 cmH2O/s). Administration of alpha,beta-methylene-ATP was followed by a significant but temporary enlargement in the bladder response to pelvic nerve stimulation to 36+/-20 cmH2O, p = 0.028, n = 7, but no change in urethral response. CONCLUSIONS At least 80% of the urethral pre-stimulation pressure was exerted by the smooth muscle. The synergic activation of the detrusor and the urethral smooth muscle in response to preganglionic parasympathetic nerve stimulation was controlled by the peripheral nerves or by the neuromuscular transmission. Administration of alpha,beta-methylene-ATP increased the bladder response to pelvic nerve stimulation without changing the urethral response.