Phenogenetic response of silver birch populations and half-sib families to separate and combined elevated ozone (O(3)) concentrations and ultraviolet-B (UV-B) radiation dozes was studied at juvenile age in the climatic chambers. Significant population and family effects were found for seedling height, lamina width, and leaf damage. The exposure to UV-B radiation decreased genetic variation at the stage of seed germination. Complex exposure to UV-B and O(3) caused an increase of genetic variation at the stage of intensive seedling growth: seedling height genetic variation in separate treatments increased from 23.7-38.6 to 33.7-65.7%, the increase for lamina width was from 10.2-13.9 to 13.6-31.8%. Different populations and families demonstrated differing response to elevated complex UV-B and O(3) exposure. Changes of genetic intra-population variation were population-specific. Such changes in genetic variation under the impact of stressors can alter adaptation, stability, and competitive ability of regenerating populations in a hardly predictive way.