summary Normal control and apparently unaffected skin from psoriatics have been compared quantitatively for their acid phosphatase activity. The unaffected skin from psoriatics shows a more rapid reaction, which may be related to a lysosomal defect. No marked differences were detected in the dehydrogenase reactions in these two tissues. However, in frankly involved psoriatic skin it has previously been shown that there is a marked increase in glucose-6-phosphate dehydrogenase activity in the transitional zone. In the present report an increase in glycero-phosphate dehydrogenase activity has been demonstrated in the lower portion of psoriatic epidermis.