The effect of time of vascular island skin flap elevation on tolerance to a subsequent 12-hour period of warm ischemia was studied. Sixty rats were separated into five equal groups; the rat epigastric island flap was used as the model.In group 1 flaps were elevated and immediately subjected to 12 hours of complete ischemia by application of microvascular clamps to both artery and vein of the pedicle. In group 2 the flap was elevated, and after 12 hours of recovery ischemia was induced for 12 hours. Groups 3 to 5 were similar to group 2 except that the time interval between initial elevation and subsequent ischemia varied: 24 hours for group 3; 72 hours for group 4; 144 hours for group 5.Necrosis was evaluated on postoperative day 7. Those flaps elevated 24 hours before ischemic insult (group 3) had significantly better survival than all other groups (p< 0.025 at least). There were no significant differences between the other groups.Flap elevation 24 hours before a complete ischemic episode significantly increased tolerance to ischemia. Elevating a flap earlier or later than 24 hours did not have any significant benefit.