The effect of treatment with intravenously administered Angiotensin II (AT II) on blood flow in normal and malignant tissues was investigated clinically. The time course of the effect of AT II was directly recorded by laser doppler velocimetry (LDV) via a probe placed on the surface of normal and malignant tissues. Intravenous administration of AT II resulted in an approximate 3.5 (1.3-14.0)-fold increase in blood flow in eleven malignant tissues, such as breast cancer with direct extension to the skin and abdominal skin metastasis of gastric adenocarcinoma. On the other hand, the blood flow in normal skin was decreased under AT II-induced hypertension, but a reactive hyperemia-like increase was observed soon after the withdrawal of AT II. These results strongly suggested that intravenously administered AT II can act as an adjuvant to enhance, by varying degrees, drug delivery to tumor tissue in cancer chemotherapy and that the administration of chemotherapeutic agents is undesirable soon after the withdrawal of AT II.