Are there reliable methods to detect, evaluate, and monitor adenine phosphoribosyl transferase (APRT) activity, 2,8-dihydroxyadenine (DHA) stone formation, and therapy of the disease? Enzyme deficiency can be characterized by radiochemically measuring the APRT activity in the erythrocyte hemolysate, thus allowing us to study hereditary factors. Using chemical methods of urinary stone analysis, 2,8-DHA stones will constantly be classified as uric acid calculi. Infrared spectroscopy enables us to clearly and reliably identify these stones. For quantitative measurements of 2,8-DHA, we have developed a specific HPLC technique in conjunction with a separating system for purine.