Introduction: Our goal was to investigate the effects of arsenic sulfur (AsS) on the detrusor smooth muscle reactivity. Material and Methods: AsS ( 100 ppm mu g/g) in drinking water was administered for 2 weeks to two groups of female Wistar rats. The contractile responses of urinary bladders to electrical field stimulation, carbachol, ATP and KCl, and the relaxant responses to ATP, adenosine and isoproterenol were examined. Urinary bladder strips were collected for light microscopic examination. Results: Our results demonstrate that oral inorganic AsS exposure induced enhanced contractile and reduced relaxant responses in rats. We hypothesize that AsS is involved in deficiencies of isolated urinary bladder in rats. Conclusion: These functional and morphological changes may be important as an intermediate link in urinary bladder oncogenesis induced by AsS. Copyright (C) 2005 S. Karger AG, Basel.