Our study includes assays of the serum activities of ALD, CPK and GOT and GPT transaminase in a patient with McArdle’s disease. Muscle glycolysis has been investigated and the glycogen concentration and phosphorylase activity determined biochemically in the muscle biopsy. Our results point to three major biochemical features which are indicative of McArdle’s disease: in the blood, the failure of venous lactic acid to rise after ischaemic exercise, and in the muscle the increase of glycogen concentration and the lack of phosphorylase activ