The effect of various winter wheat lines on the total numbers of bacteria and fungi and on the dehydrogenase and respiratory activity of soil was conducted on the basis of a field experiment. The experiment was set up on a grey-brown podzolic soil developed from loess formations with the method of randomized blocks and comprised five treatments. Soil samples for the analyses were taken in the heading, milk and full ripeness phases of winter wheat. It was demonstrated that both the microbial populations and the activity of the studied enzymes in the soil varied in the particular phases of plant growth and development, and depended also on the cultivars and lines of the crop.