The placebo effect will have a growing importance in the field of nuclear medicine as the potentials for palliative therapy with internal sources are realized. It is important for nuclear medicine physicians and their colleagues to be familiar with the role of placebo responses in clinical trials, especially when such trials involve the subjective assessment of pain. A summary of the literature on the placebo effect in pain studies is presented in which traditional values for placebo responses are contrasted with more current thinking in the field. The few published double-blind studies of pain relief after treatment with radiotherapeutic agents are summarized specifically with respect to their cited placebo response.