The applicability of serial skin surface fluorometry for repeated assessments of skin flap perfusion was investigated using the isolated perfused human transverse paraumbilical (TP) skin flap model. The flow rate, perfusion pressure and skin surface temperature were kept constant in seven human TP skin flaps and a low dose of fluorescein (3 x 10(-5) M) was used for each assessment. It was observed that the mean values for total dye fluorescence measured by a fluorometer and the maximum distance of perfusion estimated by dye fluorescein index remained consistent in five repeated assessments at 15 min interval. The variation in the maximum distance of perfusion within each TP skin flap over 5 repeated assessments was also relatively small, as judged by the mean coefficient of variation (6.1%; SEM 0.4%). Furthermore, a highly significant correlation between microsphere (15 microns) radioactivity index and dye fluorescence index was observed at corresponding locations in these seven TP skin flaps (r = 0.81; p < 0.001, n = 75). Taken together, these observations indicate that serial skin surface fluorometry provided consistent repeated assessments of skin perfusion in human skin flaps in vitro and the dye fluorescence index provided a consistent assessment of skin perfusion distance along the length of the TP skin flap. These observations lead us to speculate that critical (threshold) dye fluorescence index determined at various postoperative time points should be useful for prediction of skin viability in clinical skin flaps; thus, a clinical investigation is recommended.