A total of 75 prostate cancer and 67 lung cancer patients with positive bone scintigrams were studied. The patterns of spread in the axial skeleton and pelvis were different between the groups. The differences in the distribution of bony metastases between prostate and lung are explained by the role of Batson's vertebral venous plexus. We developed an animal model of spinal bone metastasis to prove this route. As suspension of tumor cells was injected into the tail vein of mice with vena caval occlusion. This procedure reproducibly resulted in metastatic tumor growth in the lumbar region of the vertebral column. The prevalence of spinal bone metastasis is attributed to passage of tumor cells via the vertebral venous plexus.