Nine patients with histologically proven medullary carcinoma of the thyroid (MCT) were imaged using pentavalent [99mTc]dimercaptosuccinic acid [(V)DMSA], [131I] metaiodobenzylguanidine (MIBG) and [99mTc]methylene diphosphonate (MDP). Technetium-99m (V)DMSA demonstrated most of the tumor sites in eight patients with proven metastases, with an overall sensitivity of 95% in lesion detection. Iodine-131 MIBG showed definite uptake in some of the tumor sites in three of the nine patients imaged, with equivocal uptake seen in a further one patient, with sensitivity of only 11% for lesion detection. Technetium-99m MDP demonstrated bony metastases only, in four of the patients imaged yielding a sensitivity of 61%. Technetium-99m (V)DMSA has been demonstrated in this study to be a useful imaging agent in patients with MCT, showing uptake in significantly more lesions and with better imaging qualities than [131I]MIBG, and with the ability to detect soft tissue as well as bony metastases.