The authors determined polarographically the intensity of oxygen consumption and the activity of succinic dehydrogenase of the HEp-2 cell culture infected with the association of the Cocksackie B3 with the RNA-asopositive and RNA-asonegative strains of E. coli O--111, in comparison with the uninfected and separately infected virus or control bacteria. The results were recorded 2, 6, 12, 18 and 24 hours after the infection of the cell cultures. Mixed virus-bacterial infection intensified the oxygen consumption and the activity of succinic dehydrogenase by the HEp-2 cells, followed by a profound respiratory depression. The same effect was produced by the infection of cells by the virus alone. Less pronounced was the action of bacterial component. A change in the cell repiration of the infected cultures was independent of the RNA-ase activity of bacteria. Under conditions of mixed infection the intensity of the changes in oxygen consumption and of the succinic dehydrogenase activity was determined by the viral component of the association.