Since 1927 the results of several investigations of the reaction of the blood of cancer patients (expressed as pH) as compared with normal subjects have appeared in the literature. McDonald (1), in 1927, reported that the blood of untreated or advanced carcinoma patients was more alkaline (higher pH) than normal, except in cases of skin or superficial cancers, in which it was found to be normal. In 1928, Reding (2) reported (a) that the blood of untreated cancer patients exhibits a high pH; (b) that the pH in cases of benign precancerous tumors is elevated but not to the same degree as in malignant cases; (c) that about 50 per cent of the consanguins of cancer patients show a pH slightly above normal, thus indicating a familial predisposition to cancer; (d) that the increased blood alkalinity or rise in pH habitually persists after removal of the tumor by surgery and is not due, therefore, to the presence of the tumor. The rise in pH precedes the appearance of malignancy, and returns to normal or nearly so after the patient is apparently cured by x-ray. For the latter reason, Reding considers a blood pH change after treatment to be of considerable prognostic value.