In order to determine and compare the behavior of chromed catgut and polyglecaprone 25 sutures, 49 female rats anesthetized with ether were submitted to laparotomy, cystotomy and cystorrhaphy with separate stitches using catgut for group C and polyglecaprone 25 for group E. When the bladders were observed 3, 7, 15, 30 and 50 days after suture application, stone formation was observed in 6 group C animals (p = 0.0058), with two stones (one per stitch) in 3 of them. No stones were detected in group E bladders. Microscopy revealed a similar course for the healing process and crystals were observed only in group C (p = 0.0159). We conclude that: 1) the tissue behavior of chromed catgut and polyglecaprone 25 sutures is similar, 2) catgut sutures produce lithiasis in 46.15% of the bladders sutured with it up to 50 days after surgery (p = 0.0058), and 3) polyglecaprone 25 sutures do not produce lithiasis up to 50 days after surgery.