It is generally agreed that the oral administration of griseofulvin results in the incorporation of the antibiotic into the keratinized tissues of the skin, hair, and nails. The presence of griseofulvin in these structures inhibits the growth and further invasion of sensitive dermatophytes, and results in the eventual elimination of the fungus. At the present time the mechanism by which griseofulvin is incorporated into these keratinized tissues is not known. It would appear that some of the antibiotic is firmly bound in the cornified elements, while the remainder is not so bound and may be eliminated by sweating, maceration, insensible perspiration, sebaceous secretion, or other normal functions of the skin. Gentles1 fed guinea pigs 40 mg/kg. of griseofulvin for 23 days. At the end of this period hair clippings were extracted first with water and then by refluxing with methanol. One gram of hair yielded 5μg. to 6μg. of