Ten patients with histologically proven giant cell tumour (biopsy) were imaged with 3-phase bone scanning, using 99m Tc-MDP. The perfusion (Phase I) and uptake (Phase III) were compared to the normal contralateral side and the rest of the skeleton was inspected for other abnormalities. Ninety per cent of lesions showed a doughnut-type pattern of uptake and presented with moderately increased perfusion (2.9 normal ± 0.7) and markedly increased uptake of tracer (7.5 normal ± 1.4). The patient with diffuse uptake had a pathological fracture.