The relationship between heterozygosity of 9 polymorphic loci and fertility of women surviving beyond the menopause was studied in the North-Siberian tribe Eveny. The number of pregnancies negatively correlated with the individual heterozygosity (r = -0.2913 + 0.1302, P less than 0.05). Drastic fertility reduction in heterozygous women was observed for G1M, ACP and HP loci.