Introduction - Detrusor (bladder) muscle is sensitive, in vitro, to changes in the chemistry of its environment. Changes in osmolality and potassium concentration are known to affect its contractility, as are changes in the intracellular and extracellular pH. Urine composition varies greatly both in health and in disease. It is not clear however, the extent to which the intravesical environment influences bladder function. Urodynamic testing uses a standardised filling medium, usually normal saline. This study was designed to assess the impact of changes to the intravesical biochemical environment on urodynamic testing, when compared to a normal saline control. Methods - Ninety four women, who were being investigated for lower urinary tract symptoms, consented to a repeat filling procedure. The filling phase of urodynamics was performed then repeated immediately. Each study used a test solution and a control with normal saline, in random order. The solutions used were : hyperosmolar solution; high potassium solution; a solution designed to change extracellular pH only (extracellular alkalosis); and solutions designed to affect both intracellular and extracellular pH (a hypercapnic solution to result in intracellular acidosis and a normocapnic control). Results - There were no significant effects of any changes in filling solution when compared to normal saline controls. This allowed an analysis of effect of order of fill, which also had no significant effect on urodynamic testing. Conclusions - Urodynamic testing was unaffected by changes to intravesical chemistry that are known to affect detrusor cells in vitro. This suggests that the homeostatic mechanisms of the bladder are able to maintain a stable microenvironment for detrusor cells despite changes to bladder contents.