The rationale and methods for revising the thesaurus of one of the major health sciences indexing tools are discussed. Computer production of the Cumulative Index to Nursing & Allied Health Literature and the possibility of online access mandated a revision of the list of subject headings. CINAHL has maintained a policy of responding to user needs and to changes in the nursing and allied health literature, and user input was encouraged during revision of the thesaurus. The methods of structural revision are described, and major changes in the thesaurus are detailed. Modification of the thesaurus is expected to have a far-reaching impact on the retrieval of information in nursing and allied health. Nursing and Allied Health (CINAHL) is now available online through DIALOG (file 218) and BRS (access code NAHL).