The nematode Caenorhabditis elegans was exposed over a whole life-cycle (72 h) to several concentrations of 4-nonylphenol (NP; nominal concentrations: 0–350 μg/l). Growth and reproduction of C. elegans were enhanced at NP concentrations of 66 and 40 μg/l, respectively, with effects showing dose–response relationships. These stimulatory effects might be of ecological relevance in benthic habitats, where organisms can be exposed to high concentrations of NP