Although several workers have investigated the effect on the metabolism of human subjects of adding yeast to a diet in such quantities as are commonly recommended for therapeutic purposes, the results reported have shown considerable variation. Further studies, with and without yeast, seemed important both for confirmation and additional information. Plan of Experiments: Table I shows the general plan of the 3 experiments. We studied our several subjects over longer periods of time than most workers. Breakfasts and dinners were eaten in the home of one of the subjects. Luncheons were eaten in the laboratory. The food was weighed and liquids measured. The urines were analyzed for volume, specific gravity, total nitrogen, ammonia plus urea nitrogen, uric acid, creatinine, total phosphorus, glucose, total phenols, acidity and formol titration. Blood was analyzed for N.P.N., urea nitrogen, uric acid, creatinine, total phosphorus and glucose. The feces were analyzed for total weight, moisture, total nitrogen and total phosphorus. Results: During the yeast ingestion there was an increased excretion of nitrogen and phosphorus (sum of urinary and fecal). The larger share of this excess excretion above the control periods was found in the feces, indicating a poor utilization of yeast nitrogen and phosphorus. The total urinary phenols were'less during and following the yeast periods in 5 of our 6 subjects. This seems significant, especially because the added yeast contained considerable tyrosine which is a possilde source of phenols. This decrease seems to suggest a decreased intestinal putrifaction brought abut by a change in the intestinal flora. The addition of yeast to a low protein, low purine diet after the subjects have arrived at a low uric acid elimination caused no increase in uric acid excretion. If the yeast was added while the uric acid elimination was still high, or, while the subjects were on a high protein, meat diet, an increased uric acid elimination promptly followed.