Crystalline O2-Hb was prepared according to the method of Kuhn, Birkhofer, and Quackenbush (Ber. chem. Ges. 72: 407, 1939). To obtain CO-Hb, the hemolyzed soln. of blood was centrifugalized to remove stroma, and saturated with CO. 200 cc. of the CO-Hb soln. were mixed with 100 cc. 2M phosphate buffer soln., placed in a cellophane bag and dialyzed against 3.6M phosphate buffer soln. at 5-6[degree]. The globins were obtained by pouring the O2- or CO-Hb solns. into 10-20 vols. acetone which contained 0.5% HC1. Methionine and cystine were det. according to the method of Kuhn, Birkhofer and Quackenbush. (Ber. chem. Ges. 72: 407, 1939.) Neither age. sex, blood groups nor sickness affected the methionine and cystine values for man. Human Hb contained 5.98-6.54 moles of methionine per 66,000 g. of Hb, and 2.80-3.56 moles of cystine. Similar values were found for rhesus monkeys. In cattle, methionine was 7.55-8.35 and cystine 1.24-1.85; in horses, 3.93-4.54, and 1.79-2.57; in dog, fox and jackel, 2.34-2.60 and 4.30-4.75.