The chemical and microbial characteristics of soils at seven research sites - four affected by an acid sulphate weathering and three intact, undisturbed have been investigated. The extremely low soil pH, the increased electrical conductivity and high exchangeable aluminium contents are characteristic features of the affected soils. These chemical changes were accompanied by the inhibition of the soil respiration and enzyme activities denoted the microbial activity in soils. The small microbial biomass and the abundance of bacteria and microscopic fungi indicated the worsening of living conditions for the soil microorganisms. In spite of this some representatives of microscopic fungi (Euteromycotina) isolated from the damaged soils gave evidence of their adaptability to the extreme conditions.