Alkaline phosphatase has been shown to be distributed throughout the body in various tissues and the phosphatase in serum may be one or more enzymes arising from many tissues. Investigations on calcification have consistently implicated alkaline phosphatase, but as yet no direct relationship between the activity of this enzyme and calcium metabolism has been presented. Common (1936) presented data showing that this enzyme activity increased rapidly in the serum of growing chicks fed a rachitogenic ration and that feeding cod liver oil did not cause the enzyme level to return to that of the control birds. Bell (1960) showed that the plasma alkaline phosphatase activity in laying hens and adult cocks were similar. These data showed wide variation in this enzyme activity. Much of this reported variation is no doubt due to experimental conditions such as diet, age, and state of ingested materials prior to sampling. The activity of alkaline…