In the food industry are requested speedy and accurate methods for identification of bacteria in microbiological testing of products. Molecular diagnostic methods are based on isolation of DNA from bacterial cells which is amplified in polymerase chain reaction (PCR). The result is fragment DNA about specific size, characteristic for genus or species of bacteria. The aim of the work was isolation of PCR-ready DNA. DNA has been isolated from 8 strains of genus Clostridium. Procedure of cell lysis was optimized in order to find the optimal concentration of EDTA and proteinase K in lysing buffer. DNA was isolated by phenol extraction and using magnetic microspheres. Concentrations 10 mM of EDTA and 10 l of proteinase K (100 g/ml) were the best for cell lysis for isolation of DNA by phenol extraction. Concentrations 10 mM of EDTA and 15 l of proteinase K (100 g/ml) were the best for cell lysis for isolation of DNA by magnetic microspheres. Isolated DNA was checked by gel electrophoresis, quantificated by spectrophotometry and tested in PCR. Individuals species were distinguished in denaturing gradient gel electrophoresis (DGGE).