Inflow and outflow, occlusion and perfusion pressures, and pressure in a small vein in the paw were measured simultaneously with the plethysmogram on the amputated forepaws of dogs. Venous tamponade was complete for a period of time dependent on the height of occlusion pressure and the magnitude of arterial flow. Paw venous pressure rose rapidly to 'effective occlusion pressure,' at which time blood began to escape beneath the occlusion cuff. Arterial flow began to decline immediately after occlusion. Two occlusion artifacts were observed. The first was an abrupt deflection that could be easily avoided on the plethysmogram, and the second was a slower rise that could be detected only when inflow was interrupted prior to occlusion. The plethysmographically measured flow was not significantly different from inflow measured with the electromagnetic flowmeter because of a balance between the positive error due to artifact and the negative error due to the effect of occlusion on inflow. Submitted on September 22, 1960