In epidermolysis bullosa dystrophica recessiva Hallopeau-Siemens, blister formation is due to an excessive synthesis and secretion of a genetically altered collagenase which, under mechanical trauma, becomes activated out of its pro-enzyme and leads to the destruction of collagen in the papillary dermis. There is evidence that phenytoin can inhibit the production of collagenase in the fibroblasts. This paper reports on experiences with the treatment of 6 patients suffering from this epidermolysis bullosa type with phenytoin since 2 years and more. Problems of pharmacokinetics and dosage, possible signs of intoxication, interactions with other drugs as well as side effects of phenytoin are discussed and a therapy regimen schedule is proposed on the basis of these experiences.