Two patients with prostate carcinoma and bone metastases were treated with hormonal therapy. Radioimmune imaging of bone marrow performed with 99mTc-labeled antigranulocyte antibody BW 250/183 before treatment demonstrated absence of granulopoietic bone marrow in extensive regions of the central and proximal peripheral skeleton, indicating diffuse bone marrow invasion. Bone marrow scans performed after treatment demonstrated presence of granulopoietic bone marrow in these regions, indicating bone marrow regeneration. This finding was consistent with favorable response to treatment.