The significant differences in biochemical and chromosomal characteristics, and familial history observed between group of mothers who gave birth to children affected with G1-trisomy (Down's syndrome) and their age-matched controls, indicate that these three maternal variables, in addition to the well known variable of maternal age, are associated with etiology of the aneuploidy. Since attempts to find statistical correlation between these chromosomal and biochemical variables failed, it is believed that these three are unrelated, but very possible etiological factors.