Considering the favourable nuclear properties of 99Tcm over 67Ga, we have developed a new tumour-seeking agent, 99Tc(V)m dimercaptosuccinic acid (Tc(V)-DMSA). In order to evaluate the clinical usefulness of Tc(V)-DMSA scintigraphies, 492 patients were studied with Tc(V)-DMSA, and in some cases, where possible, the results were compared with conventional 67Ga citrate scintigraphies. There was a high degree of usefulness of Tc(V)-DMSA in patients with head and neck tumours, medullary thyroid carcinomas and soft tissue tumours. But in patients with carcinomas of the lung, liver and gastrointestinal tract, malignant melanoma and lymphoma, Tc(V)-DMSA was of no or little use.