Despite appropriate microbiological surveillance and use of biocides, large quantities of bacteria and fungi have often been found in metalworking fluids. To remove these biofilm causing bacteria, two strategies are currently employed; cleaning the system before charging of fresh metalworking fluids or the use of biocides. However still there is always debate about their effectiveness and the ultimately affect on machinist health. The purpose of this study was to determine the usefulness of tetrazolium salt assay for assessment of bio-film forming capacity of microorganisms in fresh and used metalworking fluids and also evaluating their susceptibility to antimicrobial biocides. Detailed report available through Springer Link.