A biochemical analysis of acidic glycosaminoglycans in cultured skin fibroblasts of a patient with epidermolysis bullosa acquisita was carried out. Acidic glycosaminoglyans were separated from fibroblasts and culture medium and subjected to quantitative and qualitative analysis by cellulose acetate membrane electrophoresis and column chromatography. Dermatan sulfate in acidic glycosaminoglycans was eluted out with 1.25 M NaCl solution by Dowex 1 column chromatography. It was found that dermatan sulfate was increased in epidermolysis bullosa acquisita in comparison with the normal control. Then, the incorporation of 3H-glucosamine into cultured skin fibroblasts was investigated. Acidic glycosaminoglycans in the fibroblasts of the patient with epidermolysis bullosa acquisita were increased as compared with those of the normal control, although no significant differences were found in the metabolic patterns of acidic glycosaminoglycans between the patient and the normal control. Thus, it was thought that the increase in the amount of dermatan sulfate in the dermal tissue of the patient with epidermolysis bullosa acquisita was due to an excess production in the fibroblasts. It is, however, still obscure how this increase of acidic glycosaminoglycans in the dermis is related to the mechanism of the blister formation in epidermolysis bullosa acquisita.