In the article the questions concerning an actual phage problem in cheese-making are considered. The information on phages’ biology and the methods of struggle against them is announced. The results of cheese-whey samples examine on phage content selected from one of the cheese enterprises in Altai Krai are presented. The article describes applied methods of work with the systems «phage — bacterial host» and methods of reception multistrain phage-containing substrata not containing contaminating bacterial flora and keeping for a long time native properties of phage associations localized in them. The investigation presents the results of phagescreening cultures of mesophilic Lactococcus species from GNU SibNIIS collection Lactococcus lactis subsp. lactis, Lactococcus lactis subsp. lactis biovar diacetylactis and Lactococcus lactis subsp. cremoris towards phage associations situated in native whey substrata and their options received after physical and chemical treatments. The range of lytic activity and the lytic activity index of phage associations towards the experimental samples of collection cultures are determined.