The potential role of interleukin-1 in postoperative adhesion formation was examined. Cecal abrasion gave a consistently higher adhesion score when compared with sham laparotomy, on the basis of adhesion number, density, and vascularity, and so was chosen for use in further studies. The extent of serosal bleeding during cecal abrasion did not affect adhesion scores. Intraperitoneal injection of 10 micrograms murine recombinant interleukin-1 alpha in cecally abraded animals on the day of surgery and on the following 4 days resulted in a significant increase in adhesion scores when compared with those of cecally abraded animals injected with vehicle alone. Adhesions enhanced with murine recombinant interleukin-1 alpha, which were thicker and more vascular, were equivalently enhanced at doses from 10 to 10,000 ng, implying maximal response over that range. Rats not operated on and receiving recombinant interleukin-1 alpha 2 weeks after injury had increased adhesion formation. These results demonstrate that interleukin-1 alpha may be an important short-term mediator of postsurgical adhesion formation.