EN
We studied enzyme polymorphisms in a striped field mouse Apodemus agrarius (Pallas, 1771) population from NE Poland and the relationships between heterozygosity and length and mass of the digestive tract organs, and the mucosal surface area of the small intestine. _Most of 38 loci studied were found monomorphic (proportion of polymorphic loci P = 0.053, observed average heterozygosity H0 = 0.021). Heterozygotes were found for Acy, Pgm-1, Mdh-2, Est-D, Pgi, Sdh and Trf. Heterozygous males had longer large intestines and ceca and smaller liver wet mass than their homozygous conterparts. However, in females there were no significant interactions between heterozygosity and gut parameters. We suggest that the low level of polymorphism, the particular set of the loci examined and sex have an effect on detection of differences between heterozygous and homozygous individuals.