Bacterial leaching of blende flotation concentrate from Zakłady Górniczo-Hutnicze „Bolesław" was carried out using single cultures and mixed cultures of acidophilic sulphur- and iron- oxidizing bacteria Acidithiobacillus thiooxidans and Acidithiobacillus ferrooxidans. The accelerating effect of mixed cultures of bacteria on the metal leaching was amplified by correcting pH leaching medium to low values. The overall conversion of zinc exceeded 35-40%. The leaching rates of ZnS depended on redox potential, concentration of Fe(III)/Fe(II) and pH. X-ray analysis and electron scanning microscopy showed that in inoculated solution new solid phases: jarosite, elemental sulphur and anglesite were formed.