Summary1. In six cases of myeloma, the blood proteins have been studied by the method of fractioned precipitation with potassium phosphat.According to Florkin and Duchâteau, this method reveals in the normal blood serum 5 protein fractions, of which I, II and III approximately correspond to the globulins.2. The abnormalities observed in the composition of the serum were as follows :—Fraction I was 10 to 12 times higher than normal in two cases; consequently, the total proteinemia was definitely increased (96 and 117 gr. of proteins per liter). In the four other cases, fraction I was much reduced, sometimes completely absent ; the total proteinemia was normal or lowered (80 and 46 gr. of proteins per liter).—Fraction II was obviously increased in two cases (2 to 3 times the normal value).—Fraction V was decreased in three cases and reduced to 1/2, 1/3 and 1/5 of the normal value.—The other fractions showed no significant changes.3. Four of the six studied patients showed Bence-Jones proteinuria. The solubility of the urinary proteins when increasing concentration of potassium phosphate were added has been established in three of them. In one case, the urinary protein was found to be homogenous and to behave as a globulin of low solubility. In the second case, two proteins were found in the urine : one albumin and one globulin of low solubility. In the third case, three proteins were demonstrated : one albumin and two globulins rather soluble.4. There is, in this group of six cases, a correlation between the abnormalities of fraction I of serum proteins and Bence-Jones proteinuria. In the 4 cases where this proteinuria was noticed, fraction I was much lowered or absent. In the two cases where no proteinuria was found, fraction I was much increased.The significance of this correlation is discussed.