Three patients with severe recessive dystrophic epidermolysis bullosa were treated with oral phenytoin and palliative and supportive measures for variable periods. Their progress was compared with that of three milder cases managed only with palliative and supportive measures. The phenytoin-treated group showed marked decrease in blister count, increase in trauma tolerance, a rise in hemoglobin level, and considerable weight gain. The results support earlier reports that collagenase inhibitors are useful in controlling blister formation in recessive dystrophic epidermolysis bullosa.