Activity of blood cells, erythrocytes, leucocytes, and platelets, in microcirculation was observed by using an intravital microscope and confocal laser scanning microscope connected with an image processing system including fluorescence and phosphorescence emission methods. Dynamic functions of the blood flow were mainly observed in mesentery, brain, and liver tissues of rats. The results are summarized as follows: Deformability of diabetic erythrocytes was significantly lower than that of healthy controls, particularly at high shear rate. The spring constant and Young’s modulus of diabetic erythrocytes obviously stiffened, making them hard to deform in the capillary. During hemorrhagic shock and thrombosis, flow velocity and oxygen partial pressure of blood decreased in the brain and liver tissues that can be visualized by using FITC stained erythrocytes and Pd-porphyrin derivative as a pO₂ probe. Platelet adhesion and thrombus formation in the micro-vessels accelerated under the photodynamic reaction; diabetic platelets showed augmented adhesion and aggregation on the vessel wall which was followed by acute thromboembolism. Active oxygen radicals take part in thrombus formation, accompanied with adhesion of the activated leucocytes. Fluorescent dye probes, rhodamine G and acridine orange, are quite useful for visualization of the flow behavior of platelets and leucocytes, respectively.