Microbiological niacin assays were done on 34 samples of Marquis wheat, 48 of Newal barley, and 50 of Victory oats grown on gray, black, and brown soils in the years 1944 and 1945. Mean values of 53.6, 70.4, and 10.3 μgm. of niacin per gram were obtained for wheat, barley, and oats respectively. Although these results suggest that Newal barley may contain more niacin than does Marquis wheat, the results of assays conducted by a chemical method indicate that there is little difference in the mean niacin content of these two grains. Niacin levels were found to be highly variable in all three grains. Niacin and protein levels were found to be positively correlated in wheat and oats while in barley a tendency towards an inverse relation between niacin and protein was observed. No evidence was obtained to indicate that the type of soil on which grains are grown has any marked effect on the accumulation of niacin. The wheat and oat samples from the 1945 crop were richer in both niacin and protein than those from the 1944 crop, while barley samples from the 1945 crop, although richer in protein than those grown the preceding year, contained essentially the same amount of niacin.