Four laboratories were compared to ascertain the reproducibility of test methods for five bioassays: the ten day whole sediment bioassay with the amphipodCorophmm volutator, the fourteen day whole sediment bioassay with adult sea urchins Echinocardium cordatum, the Microtox solidphase bioassay with the bacterium Vibrio fischeri, the oyster larvae sediment elutriate bioassay using Crassostrea gigas and the sediment pore water bioassay with the rotifer Brachionus plicatilis. The bioassays were all conducted according to the standard operating procedures of the National Institute for Coastal and Marine Management/RIKZ and carried out with one control sediment and three moderately contaminated dredged materials from the Netherlands.