A method is presented for the simultaneous measurement of the two enzymes involved in purine salvage in human hair roots. Km values of hypoxanthine-guanine phosphoribosyl transferase (HG-PRT) for hypoxanthine and 5′-phosphoribosyl-1-pyrophosphate (PRPP) and of adenine phosphoribosyl transferase (A-PRT) for adenine and PRPP in human hair roots were similar to values reported for human erythrocytes. No differences were observed between hair root and erythrocyte enzymes with respect to the influence of magnesium and calcium ions. Heat inactivation experiments revealed comparable stability for HG-PRT, but A-PRT in hair roots is more labile than in erythrocyte