Five different suture materials (silk, monofilament nylon, polyglyconate, polyglactin 910, and chromic gut) were placed in the skin and body wall of 10 Doitsu (scaleless) koi (Cyprinus carpio). After seven days the sutures were retrieved from five of the fish in 5 mm and 6 mm punch biopsies, and after 14 days they were retrieved in the same way from the other five. The tissue reactions were evaluated by gross visual inspection and by histological examination. The total inflammatory reaction was graded on a scale from 0 (no inflammation) to 5 (severe inflammation). The synthetic suture materials generally induced a moderate inflammatory reaction that decreased after seven days. After 14 days the superficial reaction to monofilament nylon was substantial, and the tissue reactions to the organic suture materials were slightly greater than the reactions to the synthetics. The inflammatory response to silk was greater after 14 days than after seven, and chromic gut induced a moderately severe inflammatory response after seven days; the chromic gut sutures fell out before the biopsies were taken after 14 days. The organic materials induced intense inflammatory reactions which did not subside if the suture remained in the tissue.