Soil quality represents an integral value of the compositional structures and natural functions of soil in relation to soil use and environmental conditions on site. Among the indigenous soil components, different organisms and especially microorganisms play a key role in ecologically important biogeochemical processes. In that way, soil microorganisms contribute to the maintenance of the matter and energy transfer in terrestrial environments. Under stress conditions caused by adverse anthropogenic effects such as dissemination of chemical pollutants, the development and biochemical activities of soil microorganisms undergo several alterations. To prevent negative ecological consequences, microbiologically-related parameters should be involved in the indication of soil quality. In order to indicate some reliable indicators, an international project was established in which scientists from the Czech Republic, Hungary, Russia, Slovak Republic and Germany were participating. Standardized methods for selected microbiological and biochemical soil parameters were repeatedly applied in the individual laboratories on soil samples from rather unaffected and anthropogenically-affected soil sites (49 in total). After evaluation of more than 20 individual parameters it was concluded that N2-fixing bacteria, total microbial biomass, soil respiration, dehydrogenase activity, and perhaps also the humidification activity of soil microorganisms could serve as sensitive indicators of soil quality. Further research is necessary, however, to recognize critical limits with respect to the different soil types and uses. Seasonal oscillations in ecologically-related soil biological activities which regularly occur should be appropriately respected. All rights reserved.