An eight-member family is presented with two female members suffering from the juvenile form of acid maltase deficiency (AMD), the diagnosis confirmed by biochemical study of muscle. Biochemical leucocyte investigation revealed reduced a-glucosidase activity in both patients, a brother and the parents. Endocrinological study of the family disclosed reduced levels of thyroxine binding globulin (TBG) in the father and the three daughters. We consider the co-existence of AMD and TBG deficiency interesting, as thyroxine seems to play a role in the activation of acid maltase.