Evaluation of the health risks associated with the use of nanometer-sized particles constitutes an important research field. Here, the effect of gold nanoparticles (AuNPs) on human embryonic lung fibroblasts is investigated. The figure shows the uptake of AuNPs by lung fibroblasts. Most nanoparticles are endocytosed and found in vesicles (arrows) around the nucleus (N). However, some particles are found in cytosol (red circle).