Method for detection of pathogenic microorganisms in different microbiological assays (water, faeces, punctate etc.) has been developed. Device for preparation of samples and filtration of studied material through transparent tracking membranes with fixed size of pores and subsequent microscopy of filtrate was developed also as well as device for filtration of different liquids in closed cylinder under pressure. Method significantly increases informativeness and reliability of analyses, and decreases of their labor and financial costs.