Caenorhabditis elegans has emerged as an important model organism in various fields, including neurobiology, developmental biology, and genetics. Its success is due to features such as genetic manipulability, a fully described developmental program, well-characterized genome, ease of maintenance, short life cycle, and small body size. These features have led to its increasing use in toxicology for mechanistic studies and high-throughput screening. The nematode is a saprophytic species often found in soil and leaf-litter environments. It has been used as an experimental model since the publication of Brenner's seminal genetics paper in 1974. C. elegans has contributed to major discoveries in neuroscience, development, signal transduction, cell death, aging, and RNA interference. Its success as a model has attracted attention in biomedical and environmental toxicology. C. elegans is a valuable toxicity model if its results predict outcomes in higher eukaryotes. There is increasing evidence that this is the case, both at the genetic and physiological levels and in actual toxicity data. Many physiological processes and stress responses observed in higher organisms are conserved in C. elegans. C. elegans homologues have been identified for 60–80% of human genes, and 12 out of 17 known signal transduction pathways are conserved in C. elegans and humans. C. elegans is easy to maintain in the lab with a diet of Escherichia coli. Its short life cycle and large number of offspring allow for large-scale production. The transparent body allows for clear observation of all cells in mature and developing animals. The intensively studied genome, complete cell lineage map, knockout mutant libraries, and established genetic methodologies provide a variety of options to manipulate and study C. elegans at the molecular level. C. elegans is a useful model for molecular analyses of the response of conserved pathways to in vivo chemical exposure. As an in vivo model, it provides characteristics that complement in vitro or cellular models. Whole-organism assays allow the study of a functional multicellular unit, such as a serotonergic synapse, instead of a single cell. C. elegans enables the detection of organism-level endpoints and the interaction of a chemical with multiple targets in an organism. Thus, C. elegans complements both in vitro and in vivo mammalian models in toxicology. C. elegans has a number of features that make it not just relevant but quite powerful as a model for biological research. It is easy and inexpensive to maintain in laboratory conditions with a diet of Escherichia coli. The short, hermaphroditic life cycle (~3 days) and large number (300+) of offspring of C. elegans allows large-scale production of animals within a short period of time. Since C. elegans has a small body size, in vivo assays can be conducted in aCaenorhabditis elegans has emerged as an important model organism in various fields, including neurobiology, developmental biology, and genetics. Its success is due to features such as genetic manipulability, a fully described developmental program, well-characterized genome, ease of maintenance, short life cycle, and small body size. These features have led to its increasing use in toxicology for mechanistic studies and high-throughput screening. The nematode is a saprophytic species often found in soil and leaf-litter environments. It has been used as an experimental model since the publication of Brenner's seminal genetics paper in 1974. C. elegans has contributed to major discoveries in neuroscience, development, signal transduction, cell death, aging, and RNA interference. Its success as a model has attracted attention in biomedical and environmental toxicology. C. elegans is a valuable toxicity model if its results predict outcomes in higher eukaryotes. There is increasing evidence that this is the case, both at the genetic and physiological levels and in actual toxicity data. Many physiological processes and stress responses observed in higher organisms are conserved in C. elegans. C. elegans homologues have been identified for 60–80% of human genes, and 12 out of 17 known signal transduction pathways are conserved in C. elegans and humans. C. elegans is easy to maintain in the lab with a diet of Escherichia coli. Its short life cycle and large number of offspring allow for large-scale production. The transparent body allows for clear observation of all cells in mature and developing animals. The intensively studied genome, complete cell lineage map, knockout mutant libraries, and established genetic methodologies provide a variety of options to manipulate and study C. elegans at the molecular level. C. elegans is a useful model for molecular analyses of the response of conserved pathways to in vivo chemical exposure. As an in vivo model, it provides characteristics that complement in vitro or cellular models. Whole-organism assays allow the study of a functional multicellular unit, such as a serotonergic synapse, instead of a single cell. C. elegans enables the detection of organism-level endpoints and the interaction of a chemical with multiple targets in an organism. Thus, C. elegans complements both in vitro and in vivo mammalian models in toxicology. C. elegans has a number of features that make it not just relevant but quite powerful as a model for biological research. It is easy and inexpensive to maintain in laboratory conditions with a diet of Escherichia coli. The short, hermaphroditic life cycle (~3 days) and large number (300+) of offspring of C. elegans allows large-scale production of animals within a short period of time. Since C. elegans has a small body size, in vivo assays can be conducted in a