Synthetic diets containing yeast as the sole source of vitamin B and filtered butter fat as the only source of fat soluble vitamins have been shown not to give normal reproduction. The influence of single natural foods upon this function is here studied. The vitamin B content of seed (white and yellow corn, wheat, barley, and rye) was measured by growth, reproduction, and rearing of young. The data show that rats grow at the normal rate with any of these seed as the only source of vitamin B. White and yellow corn are not quite so rich in this vitamin as the other seed. Reproduction approximated the normal on these diets, but there was high mortality of young due probably to failure in milk secretion. Many 9 died during pregnancy or parturition. The amount of vitamin B necessary for normal lactation is much greater than that required for normal growth and reproduction; the amount required for reproduction is not much greater than that required for normal growth. Rats are more prolific on these diets than on synthetic diets containing either Fleischmann or Harris'' yeast as the sole source of vitamin B.