The circulating splanchnic cell and plasma volumes were measured with the regional dilution technique in splenectomized dogs under sodium pentobarbital. For a 10-kg dog, the average circulating splanchnic cell volume is 56 (SEm= 5.0) ml and the average circulating splanchnic plasma volume is 98 (SEm= 7.2) ml. These values represent 20% of the total plasma volume respectively. The splanchnic cell percentage, averaging 36.3% (SEm= 1.32%), is significantly lower than the large vessel cell percentage (average 42.4%) and is almost equal to the overall cell percentage. The splanehnic Fcellsvalue averages 0.86 and is almost the same as the overall Fcellsvalue. Therefore, the splanchnic circulation contains a portion of the total “extra plasma” in proportion to the blood volume in this region. The splanchnic mean circulation time of the plasma (average 42 seconds) is significantly longer than that of the cells (average 33 seconds).