<jats:title>Abstract</jats:title><jats:p>A ring test was carried out within the standardization process of ISO 10872 to evaluate the precision of the toxicity test for the nematode <jats:italic>Caenorhabditis elegans</jats:italic>. Eight different laboratories tested aqueous solutions of the reference substance benzylcetyldimethylammonium chloride as well as native sediments and soils for toxic effects on the growth and reproduction of <jats:italic>C. elegans</jats:italic>. Validity criteria were met in all laboratories. Average median‐ and low‐effect concentrations were determined to be 15.1 mg L<jats:sup>−1</jats:sup> (EC50) and 8.7 mg L<jats:sup>−1</jats:sup> (EC10) for growth and 7.5 mg L<jats:sup>−1</jats:sup> (EC50) and 3.8 mg L<jats:sup>−1</jats:sup> (EC10) for reproduction of <jats:italic>C. elegans</jats:italic>, with ECx values showing a high degree of reproducibility (CV<jats:sub>R</jats:sub>: <21% and <11% for EC10 and EC50, respectively) and repeatability (CV<jats:sub>r</jats:sub>: <20% and <7% for EC10 and EC50, respectively). The toxic effects of the sediments and soils revealed by the different laboratories were well related to each samples' degree of chemical contamination. Moreover, the effects showed an acceptable reproducibility (CV<jats:sub>R</jats:sub>: 5–33% and 0–28% for growth and reproduction, respectively) and repeatability (CV<jats:sub>r</jats:sub>: 3–13% and 0–12% for growth and reproduction, respectively). The present study confirms that the toxicity test with <jats:italic>C. elegans</jats:italic> according to ISO 10872 is a reliable and precise tool to assess the toxicity of aqueous media, freshwater sediments, and soils. Environ. Toxicol. Chem. 2012; 31: 1525–1535. © 2012 SETAC</jats:p>