An image processing system was developed to quantify the morphometry of nailfold capillaroscopy. Image acquisition was performed with a macrophotographic technique, and images are digitized using a video camera and an image processing system. After an image segmentation, the microcomputer determines in an interactively defined window, the following parameters: capillary loop width and length, capillary surface area, distance from the tip of the capillary loop to the dermal edge, distance between two adjacent capillaries. Other parameters can be computed from these: linear density, density and dispersion index of the distance between two adjacent capillaries (variation coefficient). A validation study, comparing 20 capillary fields from healthy subjects and 19 capillary fields with "SD-pattern", provided from patients with systemic sclerosis or dermatomyositis, reveals significant differences of all these parameters between the two groups, consistent with the literature. This study also isolates two parameters which are the best predictors of the "SD-pattern": the mean capillary surface and the capillary density (capillaries/mm2). The morphometric parameters obtained through this system are suitable for evaluation of microangiopathy and should be evaluated for diagnosis and follow-up of vascular acrosyndromes, systemic sclerosis, Raynaud phenomenon and allied conditions in clinical conditions.