Online Mendelian Inheritance in Animals (OMIA) provides up-to-date information on inherited disorders and other familial traits in non-laboratory animals. It is freely available online at http://www.angis.org.au/omia. With a strong emphasis on comparative biology, OMIA is modelled on, and reciprocally hyperlinked with, Online Mendelian Inheritance in Man (OMIM). It provides a comprehensive catalog of animal models of human inherited disorders, and also provides comprehensive access to information on potential human homologues of inherited disorders and traits in animals. Because its whole structure is based on comparative biology, it provides phenotypic information in a format that is complementary to all the relevant mapping and sequence databases now existing or being created across the animal kingdom.