The applicability of biotechnological methods to metal recovery from non-sulfide industrial waste products (slag, galvanic sludge, filter-press residue, filter dust, and fly ash) was investigated. From some products, copper, chromium, zinc or vanadium were completely extracted by sulfuric acid produced by Thiobacillus thiooxidans. The efficiency of bacterial metal solubilization varied depending on the type of waste material and on the pulp density. Stepwise increase of pulp density promoted bacterial growth and activity, resulting in metal concentrations of 6.6 g Cu/l, 6.3 g V/l, 24.4 g Zn/l or 21 g Cr/l in the leaching medium. In some cases bacterial leaching was as effective as chemical leaching with sulfuric acid. The efficiency of both processes is considered. In principal, bacterial metal recovery from industrial waste products seems to be feasible and may contribute to an increase in future supplies of raw materials, as well as to detoxification of industrial waste products resulting in reduced environmental pollution problems.