A recent survey of biotechnology-derived medicines and vaccines under development showed that the largest fraction of these were monoclonal antibodies for the detection and/or treatment of cancer. This article describes the role and function of the nuclear pharmacist in the initiation, development, and conduct of a prototype clinical trial in which a radiolabeledmonoclonal antibody (MAb) is used as a diagnostic imaging agent to detect the site of a tumor in a patient who is being managed in a hospital outpatient setting. Examples are used to illustrate selected pharmaceutical care issues in this investigational environment.