The investigation results of the cytogenetic parameters circadian rhythms in root meristem cells of birch seedlings (Betula pendula Roth.) under conditions of Altai Krai (Barnaul) are presented in the article. Seeds were collected in two city districts. Plantlets with roots of 0.5–1.0 cm length were fixed in acetoalcohol temporally with the intervals of 3 hours (from 6 am to 12 pm). Squash specimens (1 seedling — 1 sample) were used for cytogenetic studies. The overall number of viewed cells, the number of dividing cells and the cells in one or another stage of mitosis was considered. Two peaks of mitotic activity of root meristem cells in birch seedlings have been found in an ecologically «clean» area of Barnaul city: 9 am and 9 pm. Maximum values of mitotic index (MI) run up to 7.5 and 8.3%, respectively. In the morning peak the increasing of cell divisions was caused by proliferation the number of cells in metaphase, anaphase and telophase, and in the evening peak — in prophase. The increase in the mitotic index of the material collected in the city center (October Square) has been discovered. That is the evidence of the presence of stimulating agents in the environment, what are likely to be pollutants. The maximum value of MI was 9.8% at 9 am. The evening peak on this territory has not been almost revealed. Consequently, the optimal term of birch material fixation for cytological analysis of mitosis in meristem root tissue should be considered in the morning around 9 am.