Absorbable and non-absorbable suture materials were evaluated for calculi formation and tissue reactivity in the rabbit bladder. Five-O chromic, polydioxinone and polypropylene sutures were used to close cystostomies made in New Zealand white rabbits. Bladders were evaluated at 15, 30, 60 and 90 days. Calculi formed on all sutures tested and the persistence of calculi appeared to be dependent on the longevity of the suture material used. This data suggests that the use of non-absorbable suture material in urologic surgery may contribute to calculus formation.