Two protocols using the free-living nematode Panagrellus redivivus to determine the developmental or mutagenic effects of environmental contaminants were tested. Fifteen known carcinogens or mutagens, six suspected carcinogens, and seven heavy metal compounds were tested at concentrations ranging from 10−8 to 10−3 mol/L. A developmental assay using frequency of completion of the three postembryonic molts detected toxic effects of 24 of the 28 tested agents, while survival was decreased in only 10 of the 28 agents. Mutagenesis was detected in 12 of the known carcinogens, three of the suspected carcinogens, and one heavy metal compound. Therefore, assays are suitable for detection of long-term toxicity of contaminants in aquatic environments.Key words: Panagrellus, nematode, carcinogens, mutagens, developmental assay, toxicology assay