Cytotoxic and proinflammatory properties of silver nanoparticles (AgNPs) have been reported in few studies but the direct interaction between AgNPs and neutrophils, which play a key role in inflammation, has never been documented. Here, we examined the role of AgNPs with a starting size of 20 nm (AgNP20) in human neutrophils. Using dynamic light scattering for the characterization of NPs suspended under identical conditions to those used for in vitro experiments, we found that, at 10 µg ml–1, 92% of AgNP20 possess a diameter of 17.1 nm but, at 100 µg ml–1, a tri-modal size distribution with large aggregates was observed (> 500 nm). Neutrophil cell size increased when treated with AgNP20 and transmission electronic microscopy experiments revealed that AgNP20 can rapidly interact with the cell membrane, penetrate neutrophils, localize in vacuole-like structures, and be randomly distributed in the cytosol after 24 h. Treatment with 100 µg ml–1 AgNP20 for 24 h (but not 10 µg ml–1) increased the neutrophil apoptotic rate and inhibited de novo protein synthesis. We conclude that AgNP20 induced apoptosis and can act as potent inhibitors of de novo protein synthesis at 100, but not 10 µg ml–1 in human neutrophils. Copyright © 2013 John Wiley & Sons, Ltd.