Elemental silver nanoparticles were generated in polyamide 6 (PA6) by the thermal reduction of silver ions during the melt processing of a PA6/silver acetate mixture. The silver ion release from PA6 filled with 2 wt% nanosilver obeys a zero-order rate law for at least 100 days. During this time about 17 mu g silver per day, per litre immersion liquid and per cm(2) sample surface are released. The PA6/Ag-nanocomposite was shown to be active against Escherichia coli whereas the pure PA6 did not show any antimicrobial efficacy. Immersion of a nanocomposite containing 2 wt% silver in water for 100 days does not reduce its antimicrobial efficacy against Escherichia coli. Thus PA6 filled with 2 wt% nanosilver is an effective antimicrobial material for long-term applications.