Microorganisms play a unique role in the soil ecosystem because of their contribution to the soil fertility. Thus, the knowledge concerning the bioavailability (and consequently toxicity) of heavy metals in soils to microorganisms is of great importance. Traditionally the assessment of toxicity of metals has been done by measuring growth or survival of microbial population in contaminated soil. A major disadvantage of that method is that it can not discriminate between the toxicity caused by different metals or other pollutants that may be present.We have studied the bioavailabity of Pb, Cd, Zn, and Cu in metal-contaminated soils from various sources by using specific metal sensing bacteria and yeast strains. The bioavailability measurements were carried in using soil suspension without any extraction steps. The results were compared with the total metal content measured by chemical methods. Moreover, the soils were subjected to sequential extraction and the metal content of the fractions were compared to bioavailability results.The bioavailable fraction of all the metals tested was variable (of total: Pb 0,1-47%; Cu 1-62%; Cd 0,5-56%). It was in all cases, however, significantly higher than the water-extractable fraction. The soil type had a major effect on the bioavailable fraction of metals. None of the fractions of sequential extraction was found to represent the bioavailable fraction of metals.The microbial sensors used in this study are a suitable tools in helping to identify the potential biological risks of the soils even when containing total concentrations are under the permitted limit values. As there are currently no regulations for the soils containing metals below the limit values the results from bioanalyses could give additional information for any decisions to be made about the risks of these soils.