We previously reported a novel in situ observation model for microcirculation of lung metastasis from subcutaneously implanted Lewis lung cancer into mouse. Using this model, we studied the correlation of blood flow and the size of lung metastasis. It was revealed that metastatic growth and its angiogenesis are suppressed by circulating angiogenesis inhibitors, such as angiostatin or endostatin, released from primary tumor. When we removed the primary tumor, the metastasized lung cancer significantly grew faster and larger. But the blood flow per area did not increase either inside or outside of the metastatic tumor. This suggests that the growth of metastatic tumor is directly regulated not by blood flow increase but by the other effects of the circulating factors.