Blood serum Ca was studied by the method of Kramer and Tisdall. The normal range was found to be 9.4-9.9 mgm. Ca per 100 cc. In 4 cases, parathyroid administration raised the Ca above normal as long as administered; in 3 cases, only for a time, Ca dropping to subnormal in spite of continued administration; in 2 cases it was without effect. In 1 case of tetania parathyreo-priva, parathyroid administration alone had no effect on serum Ca, while combined parathyroid and Ca administration raised the Ca level. In 2 cases of normal serum Ca, Ca salts alone by mouth had no effect; in 2 cases of low serum Ca, oral administration increased the serum Ca. In 1 case of thyroid deficiency and 2 of pituitary deficiency, no effect on serum Ca was seen on administering the deficient hormones. In diabetic ketosis, and in ketosis due to diet in epilepsy, serum Ca was subnormal except in the 1st days, when it was high. Serum Ca was normal in chronic ulcerative conditions. In 3 cases of lupus erythematosus, the serum Ca level was subnormal.