It seems most unlikely that spontaneous biotin deficiency will be observed in human subjects. Although biotin is presumably an essential nutrient, not only is it present in food but it is synthesized by the intestinal flora. The amounts of biotin excreted in the urine and in the feces are greater than the intake. Current knowledge of the metabolism of biotin has been reviewed by Wright (140) . Biotin is the anti-egg white iniury factor; raw egg-white contains avidin which combines with biotin making it unavailable to the body. Sydenstricker and associates (141) produced experimental human deficiency by feeding large amounts of raw egg-white. Manifestations included anorexia, muscle pains, and dry scaly dermatitis.