Summary.1 On the basis of BODANSKY'S and LUNDSTEEN and VERMEHREN'S procedures an analytical method is described for the determination of the phosphatase activity in serum and organ extracts.2 The phosphatase activity is determined in a series of organs of normal dogs. The intestine was found to have the highest phosphatase activity, then follow kidney cortex, pancreas and, finally, liver and spleen which both have rather low phosphatase contents.3 The observations of other authors concerning the serum phosphatase activity after ligation of the common bile duct have been confirmed insofar as, a few days after ligation, a jaundice is observed which is accompanied by an increase in the serum phosphatase activity of up to c. 40 times the normal value. No parallelism is seen between the intensity of the jaundice and the serum phosphatase activity. Furthermore an increase in the phosphatase activity of the liver‐ and intestinal tissues is observed, while the stasis of the bile does scarcely affect the phosphatase contents of pancreas, spleen and kidney.4 It is assumed that the increased serum phosphatase during obstructive jaundice may originate from the