In preserved blood and during extracorporeal circulation there become formed micro-aggregates which fail to be entrapped by standard filters. The emerging there-from microembolisms provoke functional disorders in vital organs and account for unfavourable outcomes of the treatment. Basic trends in the microfiltration of the blood are analyzed, a classification of microfilters according to their design features and purpose is given, along with the medico-technical requirements they have also to meet the performance characteristics of the most wildly used microfilter models, are listed.