Fibers obtained from woven and nonwoven surgical fabrics were operatively instilled into the peritoneal cavities of rats to assess pathologic responses at 2, 8, 16, and 32 weeks postoperatively. Adhesions were found in 20% of the sham-operated animals and in 22% and 29% of the animals with fibers from woven and nonwoven fabrics, respectively. These differences were not significant. The adhesions were not progressive with time and were not related to increased morbidity or mortality rates. Foreign-body granulomas were found in 8% of the sham-operated animals and in 96% and 89% of the animals with fibers from woven and nonwoven fabrics, respectively. Differences between the groups with fibers were not significant. There were no morphologic differences in the granulomas of woven and nonwoven materials; they did not increase in number of enlarge with time. We conclude that responses to cellulose fibers, whether from cotton or from nonwoven materials produced from wood fibers, are virtually identical.