Adenine nucleotide concentrations and metabolism in red blood cells (RBC) and RBC ghosts from psoriatic patients and healthy subjects were compared. 2. The ATP and total adenine nucleotide levels and the adenylate energy charge (EC) were elevated in the blood from psoriatic patients. 3. The rate of glycolytic production of ATP by intact RBC was unchanged, but the Na+, K(+)-ATPase activity of RBC ghosts was decreased significantly in psoriasis. 4. Results suggest that the defect in adenine nucleotide metabolism is a systemic manifestation of psoriasis, and that the quantification of adenine nucleotides in RBC and in whole blood samples may be of pathophysiological value in psoriatic lesion.