A diet containing 14.7 per cent of crude protein, obtained from rolled oats and bran in the ratio of 2:1, butter fat and salts, has been described. This is about the maximum amount of dietary protein possible to obtain by using these raw materials. It would appear that this diet is perfectly satisfactory for the nutribiton of guinea pigs, and that it contains considerably more than a minimum of the known essential amino acids. The survival time on this diet alone of guinea pigs standardized by previous preliminary feeding of large amounts of vitamin C, has been found to be 28 to 34 days (average 30.2±1.8) for animals weighing 400–500 gm., and 26 to 33 days (average 29.2±2.0) for animals weighing 250–350 gm. Some data obtained with this diet, when it was cooked in alkaline solution previous to feeding, indicate that it contains no detectable amount of vitamin C. It appears not improbable that it contains absolutely none. A few preliminary experiments with dried brewer's yeast in large concentrations indicate that it is possible to use this material as a bearer of vitamin B in scurvy diets without fear of adversely affecting the guinea pigs or without the introduction of detectable amounts of vitamin C. We would not recmmend it in large concentrations as a protein supplement on account of the taste. The diet of oats and bran would appear to be eminently suited for animals placed in acute qualitative tests of materials which contain only trances of, or no, vitamin C. It would probably serve for the longer 90 day tests except that, for the present, expediency rather than demonstrable necessity would dictate that we supplement it with both protein and vitamen B complex. In view of the difficulty and uncertainty of obtaining final convincing evidence that would entirely suffice, it will be better in the future to direct attention to such supplementation. Attention has been called to the unreliability of the negative control test and the possible fallacies in the results therefrom. It would be well for the investigator, if he is inclined even by tacit implication to insist on adiet free of vitamin C, to avoid the dilemma of being unable to prove from his tests whether the diet or the animals he is using are satisfactory. It is possible that at an early date this test may revert to its proper status, namely, one of animal rather than dietary control. Even though it is logically to be presumed that all commerical rolled oats, bran, and dried brewer's yeast are free of disturbing amounts of vitamin C, we would nevertheless recommend a test of such materials before using as well as the preparation of the diets from large uniform batches of raw materials.