An increasing focus in health care is the development and use of electronic medical record systems to capture and store patient information. T-HELPER is an electronic medical record system that health care providers use to record ambulatory-care patient progress notes. These data are stored in an on-line database and analyzed by T-HELPER to provide users with decision support regarding patient eligibility for clinical trial protocols and assistance with continued protocol-based care. Our goal is to provide a system that enhances the process of identifying patients who are potentially eligible for clinical trials of experimental therapies in a clinic that is limited by the existence of a singular clinical trial coordinator. Effective implementation of such a system requires the development of a meaningful controlled medical terminology that satisfies the needs of a diverse community of providers all of who contribute to the health care process. The development of a controlled medical terminology is a process of identification, collaboration, and customization. We enlisted the help of collaborators familiar with the proposed work environment to identify user needs, to collaborate with our development team to construct the preliminary terminology, and to customize the controlled medical terminology to make it meaningful and acceptable to the clinic users.