The effects of piroxicam on postoperative changes of collagen – measured as hydroxyproline – concentrations were measured around intestinal anastomoses in rats. Piroxicam, in a dose of 2 mg/kg/day, significantly reduced the decrease of hydroxyproline concentrations around colonic anastomoses during the first 3 days after the operation but also reduced the increase of hydroxyproline concentrations observed at day 7 around ileal anastomoses in the control group. 10 mg piroxicam/kg/day resulted in a 100 % lethal peritonitis after the 5th postoperative day. We suggest that piroxicam affects collagen metabolism by inhibiting granulocyte functi