Escherichia coli and Saccharomyces cervisiae suspensions were submitted to controlled shear stress. Above a threshold value shear stress induced a decrease in micro-organism viability. The threshold of shear stress efficiency depended on the micro-organisms, being between 1292Pa and 2770 Pa for S cerevisiae, and about 1250Pa for E coli. Above 1810Pa, E coli cells were disrupted whereas the S cerevisiae cells remained intact. The higher the cellular concentration, the greater the rate of decrease in viability. Viability loss was influenced by the number of passages through the experimental shear stress device and by exposure time.