UW solution has been found to be an effective organ perfusate for transplantation. Initial studies in experimental pedicle skin flaps have also demonstrated its unique effectiveness in prolonged ischemia. To understand better the limits of its preservation properties without the influence of endothelial clamp damage, we have undertaken to study the properties of UW solution in experimental microvascular free flaps. Control, lactated Ringer's, and UW solutions were utilized in pedicle and microvascular free flaps in Sprague‐Dawley rats over varying periods of ischemia. UW solution demonstrated a clear superiority over all other solutions in both flap models. In addition there also was a significant prolongation of critical ischemia time in UW‐treated free flaps compared to pedicle flaps. © 1993 Wiley‐Liss Inc.