White atrophy (atrophie blanche) in the medial ankle region due to chronic venous insufficiency (stasis syndrome) was studied in 12 patients by fluorescence video microscopy [1,8]. After intravenous bolus injection of 1 ml of 20% Na-fluorescein the dynamic phenomena of transcapillary and interstitial diffusion of the dye were analyzed by a videodensitometer which has moved on single frames of the TV-recordings across white atrophy at different times after dye appearance. White atrophy is characterized by 3 main areas: 1) the avascular field sensu strictu, 2) the border region with enlarged and tortuous capillary loops, and 3) the more remote capillaries showing less altered morphology. The dye reached the ankle skin after 39.2 +/- 13.3 S and leaved rapidly the intravascular compartment. In the region of the border capillaries, the maximal fluorescent light intensity was reached after 5 min, in the centre of the avascular field only after 40 min. Initially, the densitometer curves show a 'valley' which is slowly filled up by the dye. At 40 min and later on the highest light intensities were measured in the central parts of the avascular field ('mountain'), where the clearance was just beginning. The slow diffusion of the small tracer into the avascular field explains that white atrophy is a predilection site for venous ulcer formation.