In clinical practice, it may be difficult to distinguish a metastatic bone superscan appearance from a normal bone scan. To determine if assessment of bone marrow is helpful in the diagnosis of bone invasion in patients with suspected bone superscans, the authors performed antigranulocyte antibody bone marrow scans in 10 consecutive cancer patients who had a conventional bone scan interpreted as metastatic superscan appearance. All patients presented with bone marrow scans showing marked absence of tracer uptake in the central skeleton suggesting tumour replacement. Laboratory tests showed decreased peripheral blood cells in 9 patients. Bone radiographs showed metastatic involvement with diffuse osteoblastic lesions in 9 patients. Antigranulocyte bone marrow scans show extensive bone marrow invasion in cancer patients with suspected bone superscans. This result reinforces the concept of these patients having extensive bone invasion despite mild abnormalities in the bone scan. Confirmation of extensive bone invasion on patients with suspected bone superscans may contribute to a proper staging of these patients.