The patient-care activities of a pharmacist in a thyroid clinic are described. Since 1978 a pharmacist has been an active member of the staff of a thyroid clinic associated with a 500-bed university hospital. More than 1500 patients are referred to the clinic each year. The pharmacist initiates, maintains, or modifies the drug therapy of selected patients with physician-diagnosed thyroid disorders under the guidance of written protocols approved by the chief endocrinologist. Most patients treated by the pharmacist are receiving thyroid-suppression therapy, antithyroid drugs for Graves' disease, or thyroid hormone supplementation after surgery or after radioactive iodine therapy. The pharmacist assesses patients, prescribes medications, orders laboratory tests, charts visits and therapeutic plans, and educates patients about their conditions. Major changes in thyroid status and drug therapy are always discussed with the chief endocrinologist. The pharmacist also participates in educational programs to influence prescribing by physicians, provides drug information, serves as a preceptor to pharmacy students, and is investigating the equivalence of levothyroxine preparations in vivo and in vitro. An audit of patient outcomes showed that the pharmacist is highly effective in her role as a giver of direct patient care. A pharmacist's role in a thyroid clinic can consist of clinical practice, education, preceptorship, and research.