The results of the comparative investigations of basic hydrodynamic parameters and k(L)a coefficient in three types of commercial laboratory bioreactors (stirred tank, bubble column and air-lift) are presented. The investigated fermenters belong to the same installation BIOSTAT ED (B.BRAUN BIOTECH, Germany) and have the same working volume of 15 dm(3). Biological evaluation of the applicability of these fermenters to carrying out various biotechnological processes was also performed. The biological testing systems were yeasts K. fragilis used in the processes of whey utilization and filamentous fungi A. niger used in citric acid biosynthesis. It was found that the biological evaluation of bioreactors is an important element in selecting a proper equipment for specific biotechnological process.