A comparative examination of the hair of the members of a family with monilethrix was carried out. Scanning electron microscopy (SEM) was used in the examination. It could be shown that the hair of persons with monilethrix showed a clear irregularity in its surface structure. A corresponding pattern was found in the clinically healthy sister and the likewise healthy father. The surface of the mother’s hair showed a normal condition. The cuticle of the monilethrix appears to be very soft. The SEM method permits more exact examinations concerning the heredity of monilethri