Use of the human genome sequence in disease therapy will require efficient identification of disease-causing and disease-associated genes with functions that are amenable to pharmacological manipulation. The validation and development of such genes as therapeutic targets requires information about both the genes' functions and the biochemical pathways in which they participate. One powerful means of obtaining such information is the study of homologous genes in model organisms amenable to laboratory manipulation. Among model organisms the nematode Caenorhabditis elegans offers several advantages, including well-established techniques for genetic and experimental manipulation and the first completed genome sequence for a multicellular organism. Molecular genetic experiments using C. elegans can contribute at several levels to drug discovery programs, from elucidation of genetic functions and pathways to the validation of candidate targets. Additionally, the ease of culture allows adaptation of the nematode for use in high-throughput chemical screens for the identification of lead compounds in drug development.