Painting a glass slide with branched or linear N,N-dodecyl methyl-polyethylenimines (PEIs) and certain other hydrophobic PEI derivatives enables it to kill influenza virus with essentially a 100% efficiency (at least a 4-log reduction in the viral titer) within minutes, as well as the airborne human pathogenic bacteria Escherichia coli and Staphylococcus aureus. For most of the coating polyions, this virucidal action is shown to be on contact, i.e., solely by the polymeric chains anchored to the slide surface; for others, a contribution of the polyion leaching from the painted surface cannot be ruled out. A relationship between the structure of the derivatized PEI and the resultant virucidal activity of the painted surface has been elucidated.