In a field experiment, changes taking place in the soil environment under cultivation of two winter rape cultivars, Casoar and Californium, after the application of the chemical preparation Reglone 200 SL were determined. The soil belonged to black earths proper (WRB-Mollic Gleysols) with pH 6,1. Conducted research indicated that the chemical agent Reglone 200SL, extensively used in plant protection, with the passage of time disturbed the biological balance of the soil. As a result, the number of investigated groups of microorganisms was decreasing. Term of analyses caused a significant increase of ureolytic activity of the soil and a significant decrease of proteolytic activity. The herbicide applied only slightly modified the ammonification and nitrification processes, and the rape cultivars used in the experiment determined the differences in the numbers of bacteria with proteolic aptitudes and in protease activity.