Tissue reactions to natural and synthetic braided and monfilament suture materials in gingiva and oral mucosa were studied. A total of 138 sutures made of four commonly used materials were placed in the edentulous ridges and vestibutlar mucosa of eight beagle dogs. Biopsy specimens including the suture loop and surrounding tissues were obtained after 3, 7, and 14 days and processed for histolgoic analysis. The inflammatory reaction was more rapid and intense than the reaction that has been reported after suture placement in skin. Bacterial invasion of the sutu re track was a common sequela regardless of the material used, but it was particularly prominent for silk. The formation of a perisutural epithelial sleeve was well under way at 3 days and in some instances included the entire suture track within 7 days. Connective tissue reactions consisted of several well-defined, concentric perisutural zones. At 14 days, these zones were partly replaced by granulation tissue surrounded by a fibrous capsule. The synthetic monofilament suture elicited a mild inflammatory tissue response. The results showed that sutures placed in gingiva and oral mucosa produce a prolonged tissue response that is most likely a result of the continual influx of microbial contamination aslong the suture channel, which may be a lesser problem when sutures are placed in other surgical compartments. The results indicate that chromic gut sutures are rapidly and unpredictably absorbed when used in an environment characterized by moisture and infectious potential.