We investigated morphology of skin capillaries and pericapillary halos and transcapillary diffusion of Na-fluorescein in 15 patients with mild chronic venous incompetence (CVI) and in 15 healthy controls. Transcutaneous fluorescence videomicroscopy was performed at the medial ankle region. To assess transcapillary diffusion the fluorescent light intensity was monitored within a densitometer window encompassing 3.2mm2 of skin surface. Only a few capillaries exhibited the features of microangiopathy described in patients with severe CVI. A minority of microvessels of the patients with mild CVI showed moderate dilations or increased tortuosity. Inhomogenous perfusion, extremely tortuous microvessels resembling glomeruli, obliterations of vessels or avascular fields frequent in severe forms of the disease were not detected and the density of skin capillaries was identical to controls. Although skin capillary alterations were mild or moderate, mean diameter and range of pericapillary halos were significantly (p less than 0.05) enhanced in the group with mild CVI, indicating increased transcapillary diffusion. This finding contrasts to the results in healthy volunteers and to the values previously measured in patients with severe CVI, in whom normal fluorescent light intensities were determined in skin areas of identical location and size. We conclude that in mild CVI enhanced transcapillary diffusion predominates, while morphological alterations of capillaries typical for severe CVI are just beginning to emerge.