Abstract: Microcirculation of nail fold has been observed and plethysmography has been measured after x-ray irradiation in 5 patients with tumor.Plethysmography showed marked changes such as increased blood flow, vasodilation in the exposed field 3 days after irridiation. However, blood flow decreased markedly 25-35 days after irradiation than before. There were similar changes in microcirculation in area without irradiation. Microvessels were dilated, vasomotion was increased with aggregation of erythrocytes in the nail fold 3 day after irradiation. Coufiguration of microvessels also changed markedly. Vascular loops become shorten and thinner 35 days after irradiation.