Intensive microbial growth on 4 nutrient media (containing glucose, starch, nutrient broth or peptone + yeast extract) in soil suspension experiments, changing pH (acidification or alkalization) caused partial liberation of Cd sorbed by soil particles to liquid phase. At the same time a considerable transformation of the solid phase Cd to soluble in 0.1 N NaOH form was observed. Increased Cd concentration in the alkaline extract was accompanied by decrease of the heavy metal extractability with DTPA. The mechanisms which might be responsible for the observed phenomena are discussed. The obtained results suggest that microbial action can simultaneously increase and decrease availability of Cd to plants.