Chitin is a polymer of D-glucosamine, beta-poly-N-acetyl D-glucosamine. The chitin derivative, 70% deacetylated chitin (DAC-70), shows immunopotentiating activity. DAC-70 ointment 3.5% in a white petrolatum base was used to treat defined areas of four patients with senile exfoliative erythroderma following eczema. The effects of DAC-70 were compared with those of glyteer (0.2% soybean tar ointment) with 0.1% dexamethasone. In all patients erythroderma ceased spreading within 1 to 2 weeks in all treated areas. Thus, topically applied 3.5% DAC-70 may be of similar value to glyteer in the treatment of exfoliative erythroderma following eczema.