Kallmann's syndrome is a rare condition defined as a combination of hypogonadotropic hypogonadism and anosmia. The present study shows two genealogical tables. In the first family six male members in four generations had Kallmann's syndrome. All carrier females seemed to have normal fertility and normal olfactory function. X-linked recessive or - less probable - dominant sex linked inheritance was considered to be most probable. Renal malformation was discovered in one and was excluded in two affected members. In the second family only one affected female was discovered. She had a monozygotic twin sister with normal pubertal development, but also total anosmia. Four individuals with anosmia alone were found in this family, but no further cases of hypogonadism. The possibility of an acquired hypothalamic insufficiency on the basis of hereditary anosmia is discussed.