The results of immunoscintigraphy of haematopoetic bone marrow were compared with those of conventional bone scanning in 141 patients with malignant diseases. Marrow scans showed more metastatic lesions than bone scanning in all patient subgroups, resulting in a significantly more extended skeletal involvement. CT was concordant in 83.3% of 323 skeletal regions with bone marrow scanning. Bone marrow scans of 30 control patients with benign disease were abnormal only in 7 of 2135 skeletal regions in 3 patients. In malignant lymphoma, bone marrow histology or aspiration cytology was concordantly positive in 14 or negative in 17 patients. Immunoscintigraphy of haematopoetic bone marrow provides a reliable, sensitive and safe novel approach towards the non-invasive evaluation of metastatic spread to the skeleton.