The Mutant Mouse Regional Resource Center (MMRRC) repository simple and advanced search methods now include the ability to search by associated Major Medical Subject Heading (MeSH) terms. MeSH is the National Library of Medicine\'s controlled vocabulary thesaurus. It consists of sets of terms naming descriptors in a hierarchical structure that permits searching at various levels of specificity. Major MeSH terms are defined by authors of primary research articles as having the most relevance to the research represented by the article.