Grassing and the development of deciduous stands on the ridge of the Ore Mountain, NW Bohemia, contributed dramatically to the improvement of microbial conditions in the soil: the concentrations of heterotrophic bacteria were increased by 1-2 orders and soil respiration, ammonification and nitrification also increased. Less marked were changes in soil enzymatic activities. CO2 immissions cause no long-term soil intoxication that would hamper microbial life.