Disclosed are compositions comprising a) an antimicrobial agent, which is selected from the group consisting of biocides containing halogen atoms and/or containing phenolic moieties, formic acid, chlorine dioxide, chlorine dioxide generating compounds, dialdehydes; components containing an antimicrobial metal such as antimicrobial silver, and b) a polyamine, especially a polyethylenimine. The polyamine is effective as a booster for the antimicrobial agent.