In random pattern skin flaps of mice, tissue fluorescence measured by means of videodensitometry at 24 h after flap elevation significantly correlates with intravital microscopically measured functional vessel density and viability of skin tissue as assessed by transmission light and electron microscopy. The correlation was found reproducible in non-ischaemic flaps (r = 0.86) and flaps being rendered ischaemic for 6 h after elevation (r = 0.98), indicating that increased microvascular permeability as a result of ischaemia/reperfusion does neither affect tissue fluorescence nor the accuracy of the fluorescein dye test. In addition, tissue fluorescence at 24 h after flap elevation accurately predicts ultimate flap survival on the 7th postoperative day with a sensitivity of 0.89 and a specificity of 0.85. These results suggest that in non-ischaemic as well as in ischaemic random pattern skin flaps tissue fluorescence can be used for assessment of nutritive blood flow, viability of skin tissue and ultimate tissue survival in these flaps.