The relation between the capacity of the animal body to destroy morphine and its power of developing tolerance to the drug following repeated dosage has been of interest to pharmacologists for many years. Recent study with the aid of improved chemical methods indicates that Faust's1conclusion, that a direct, casual relationship between the two phenomena exists, is incorrect. It seemed important to collect from human material such data as might bear on this subject. The study here reported concerns the excretion of morphine by human addicts; the difference between the amounts of morphine administered and those excreted is to be regarded as a measure of morphine destroyed. While it is well known from the early observations of Kauzmann,2Vogt,3and Jacques4that morphine is eliminated in the urine and feces of human addicts, its quantitative excretion in these channels has, to our knowledge, not been studied. In the subjects whom