Photoplethysmography(PPG) employs an infrared light-emitting diode to transmit light into the skin noninvasively. Light reflected from blood cells is received by a photocell or phototrotransistor which permits recording of the pulsatile cutaneous microcirculation. The use of PPG for vascular measurements in extremities is not new. Since Hertzmann, in 1938, first described the technique to measure skin blood flow, a few investigators have used PPG for clinical application. However, experimental reports on the photoplethysmographic assessment of blood flow after arterial reanastomosis are rare. We assessed the changes of blood flow after reanastomosis of the femoral artery in rabbits using photoplethysmography. We divided 20 rabbits into 3 experimental groups. In Group I, the femoral artery was surgically exposed and clamped for 60 minutes. In Group II, the femoral artery was surgically exposed and clamped, as in Group I, and then severed and anastomosed crudely in order to creat thrombus formation. In Group IU, the femoral artery was prepared as Group II and then anastomosed carefully to ensure patency. Blood flow was measured by photoplethysmography on the anteromedial aspect of the right hind leg, every 15 minutes for the fisrt 2 hours, at the 3rd day, I week, and II weeks post-operatively. The following results were obtained l. After the removal of vascular clamp, the mean time for the pulse wave to return to normal form was 63±24.0 minutes in Group I and 63±18.7 minutes in Group III. There was no statistically significant difference beween the two groups. When the wave form was normalized, it remained so continuously. 2. After the removal of vascular clamp, the mean time for the wave amplitude to return to normal was 108±11.2 minutes in Group I and 102±16.4 minutes in Group III. There was no statistically significant difference between the two groups. 3. The thrombosis which obstructed blood flow was formed within the first 60 minutes(mean time: 49±12.4 minutes) in all the animals in Group II. When the thrombosis was formed, it was readily detected by the change of wave form and by decrease in amplitude. 4. It is concluded from this experiments the changes of blood flow after reanastomosis of the femoral artery in rabbits were accurately assessed by PPG. It is suggested that PPG can be used clinically in monitoring blood flow after arterial reanastomosis.