Wound healing in the stomach and colon of mongrel dogs was studied using physical, histologic and chemical techniques to evaluate effects of various suture materials on the healing pattern and to compare visceral wounds with skin wounds. The general pattern of healing for stomach and colon wounds is the same in rats, rabbits and dogs. However, the extent of healing, the percentage of strength of normal tissue attained by the wound, is less in the dog than in the rat or rabbit. Prolene and plain and chromic catgut produce the least and silk produces the greatest cellular reaction in the stomach and colon. We believe the effect of absorbable sutures on strength of stomach and colon wounds, while statistically significant, is not of any great clinical significance except perhaps in severely debilitated patients. A trial of Prolene sutures for anastomotic closure would seem indicated. The healing of stomach and colon wounds differs from the pattern observed for skin wounds. Breaking strength increases rapidly for 14 to 21 days postwounding and then does not change significantly. The wounds are metabolically more active than skin wounds since the rate of collagen synthesis is markedly elevated even after 120 days and the rate of noncollagenous protein synthesis is twice as great in the wound as it is in normal tissue. Colon and stomach wounds closed with absorbable sutures are weaker at 14 through 28 days than similar wounds closed with nonabsorbable sutures. Yet, when strength of wound is expressed as a percentage of strength of unwounded tissue, there is no difference between wounds blosed with absorbable or nonabsorbable sutures. Thus, it would appear that there is a general diminution of the strength of normal stomach and colon wall up to 6 centimeters from wounds which have been closed with absorbable sutures.