The benefit of perfusion washout in both experimental and clinical skin flaps has long been debated. By perfusing ischemic rat pedicled flaps with UW solution, a recently developed, high-molecular-weight, organ-preservation medium, a 170 percent increase in the critical ischemia time of treated versus untreated control flaps was demonstrated. Sixty rats were used in this study. A 3- x 6-cm unilateral abdominal skin flap based on the superficial inferior epigastric artery and vein was raised. The flaps were divided into three groups: Group 1 (control) - no perfusion washout (n = 15); Group 2 (LR) - perfusion washout with lactated Ringer's solution (n = 15); Group 3 (UW) - perfusion washout with UW solution (n = 30). Flaps were subjected to varying periods of ischemia, ranging between 8 and 30 hr. The primary ischemia time at which 50 percent of the flaps survived clinically was 10 hr for Group 1, 15 hr for Group 2, and 27 hr for Group 3. The differences between the survival rates for flaps in Groups 1, 2, and 3 were statistically significant (p < .0005). By bathing the vascular and parenchymal cells in an impermeant preservation solution, it was hypothesized that cellular swelling would be inhibited, thereby significantly improving a skin flap's tolerance to warm ischemia. Furthermore, after reviewing the pertinent literature, it is evident that the primary critical ischemia time of 27 hr is the highest reported to date for the normothermic experimental rat pedicled flap. Clinical application of these findings, as well as the need for further studies, are discussed.