Toad red blood cells were used to measure regional bone blood flow in the canine mandibular ramus. The blood cells were labelled with sodium pertechnetate and fixed in 1 0%formalin; they were 22 × 15 μm in size and had a specific gravity close to that of dog red blood cells. These cells had no discernible effect on systemic hemodynamics after injection

did not agglutinate

were well mixed and evenly distributed throughout the body

and were completely extracted in one circulation through the mandible. The mandibular ramus was divided into six regions. and the blood flow rates in each were found to be similar to those reported in previous studies with radiolabelled carbonized

microspheres. Furthermore

the blood flow distribution pattern of the mandibular ramus determined in this study was identical to that of our previous study using the bone-seeking radionuclide method. We suggest that radiolabelled toad red blood cells are an ideal marker for measuring regional blood flow in the canine mandible.