MRC-5 fibroblasts infected with human cytomegalovirus (HCMV) reference strain AD 169 were treated with different concentrations of methylated alpha-lactalbumin (Met-ALA) or methylated beta-lactoglobulin (Met-BLG), as well as with their peptic hydrolysates, and with the highly basic polypeptides such as are L-polylysines (4-15 kDa). The antiviral activity was calculated by comparing the number of infected cells in the presence and absence of the tested substances. Both Met-ALA and Met-BLG, as well as their peptic hydrolysates, decreased the infectious activity of cytomegalovirus in fibroblast cells. As expected, L-polylysines showed the highest antiviral activity. However, the tested basic proteins and polypeptides despite their lower antiviral activities might be potentially quite useful in fight of arising drug resistance activities and the persistence capacities of this virus.