Fiberoptic: perfusion fluorometry and assessment of ultimate viability were used to analyze the tolerance to warm ischemia of rat vascular island skin flaps. Both acute flaps and flaps raised 24 hours previously and then reraised were subjected to 0 (control), 6, 8, 10, and 12 hours of vascular pedicle clamping. Following clamp release, serial fluorometry documented the progressive delay in effective reflow resulting from extended periods of ischemia. Fluorometry, furthermore, suggested that flaps constructed 24 hours previously had an improved hemodynamic status with a significantly reduced period of pool reflow following clamp release. The improved hemodynamics were associated with increased viability, confirming the increased tolerance of 24-liour-old flaps to warm ischemia.