Vasilyev A. G. and Vasilyeva I. A. 1995. Non-metric variation in red vole populations within the East-Ural Radioactive Track (EURT) zone. [In: Ecological genetics in mammals II. G. B. Hartl and J. Markowski, eds]. Acta Theriologica, Suppl. 3: 55-64. Ecological monitoring of red vole Clethrionomys rutilus (Pallas, 1778) populations, carried out for two years (1992-1993) in the Sverdlovsk region near Kamensk-Ural'ski, revealed an increase of morphological diversity in terms of non-metric skull traits along the axis of the East-Ural Radioactive Track (EURT). In the population affected by radioactive contamination, frequencies of non-metric skull traits deviated significantly from those in two control populations located beyond the EURT boundaries. The deviations were not related to particular environmental factors varying among the years of our study, which implied a genetic basis of non-metric differentiation. We suggest that the observed increase of phenotypic malformations within the EURT zone has been caused by the permanent impact of low doses of radioactive contamination, leading to an accumulation of minor mutations and to disurbances in regular ontogenetic development of the red vole.