Numerous disorders of the lower urinary tract observed in children, such as dysfunctional voiding, infections or vesicoureteral reflux, may be caused by defective synchronization between the central nervous system and the activity of the lower urinary tract. The analysis of acetylcholine and acetylcholinesterase's activity - the mediator and inhibitor of neurotransmission in the parasympathetic nervous system - can provide a lot of information concerning the extent to which the anomalies have developed and the possibility of pharmacological correction of the aforementioned lower urinary tract pathology.The aim of the study was to determine the role of the parasympathetic nervous system in the pathological creation of vesicoureteral reflux.Material and methods. This study was conducted between the years 2000 and 2004 in the Clinic of Pediatric Surgery and Urology of Wrocław Medical University. Thirty children who underwent surgical correction of vesicoureteral reflux underwent full-thickness biopsy of the bladder wall during the procedure. In each case, the biopsy was taken from the top of the bladder incision used to perform uretrocy-stoneostomy; those children formed group "0". Nineteen children with neurogenic dysfunction of the lower urinary tract who had bladder-augmenting surgery also underwent biopsy from the top of the bladder incision; those children formed group "N". Results of the bladder wall's tests of 6 children who have undergone surgery to open the bladder for a different reason than vesicoureteral reflux were also analyzed (control group - K). The biopsies of the bladder wall were put on ice and immediately sent to the Immunohistochemy Laboratory of the Pathological Anatomy Institute of the Medical University in Wrocław. These samples underwent a reaction with monoclonal antybodies against acetylcholine and acetylcholinesterase to determine acetylcholine and acetylcholinesterase activity. Because of considerable difficulty in objective determination of the intensity of the colour reaction, an arbitrary division into three structural areas of the bladder was introduced:- epithelium- blood vessel endothelium- muscle layerIn order to interpret the results of the tests, a statistical analysis was performed.Results. Statistical analysis of the results shows a strong correlation between the occurrence of bladder instability and ACH stimulation in the bladder wall's muscle layer, both in children with vesicoureteral reflux and with neurogenic dysfunction of the lower urinary tract. A similar reaction occurs with ACHE and bladder instability. Degrees of this correlation suggest a strong cause-and-effect relationship between parasympathetic activity and the bladder instability phenomenon. One could ask at this point if it is caused by too much ACH or not enough ACHE activity. The performed analyses indicate that both processes are present.Conclusion. One of the preconditions of vesicoureteral reflux occurrence is excessive stimulation of the parasympathetic nervous system in bladder wall epithelium.