The effects of laser irradiations have been estimated both from the clinical point of view (rate of reduction of the ulcerated area) and in ultrastructural terms. The modification produced by laser in human fibroblasts in culture have also been investigated. Under our clinical and experimental conditions, laser stimulates the secretion of fibroblasts, both in vivo and in vitro, for reasons that are still the object of research. After irradiation the formation of periodic collagen fibrils is not observed, so that complete ‘restitutio ad integrum’ of the dermal matrix does not occur.