IN 1957, Axelrod reported that epinephrine and norepinephrine were O-methylated at the C-3 position, giving metanephrine (3-O-methylepinephrine) and normetanephrine (3-O-methylnorepinephrine), respectively, in the rat1 ; in addition, he found that these compounds were normally excreted in rat urine2. The excretion of normetanephrine in the urine of humans with pheochromocytoma has also been reported3. More recently, the importance of the pathway for 3-O-methylation of epinephrine has been confirmed in man4. This report concerns the identification of metanephrine and normetanephrine of endogenous origin in the urine of normal human males.