Contributions of total underground biomass to total soil respiration in a tallgrass prairie are evaluated by 2 independent techniques and compared to values previously obtained at the same study site by a 3rd method. Root contribution to total soil respiration measured by compartmentalization of isolated soil cores in the laboratory estimated root contribution to be 29.5% of the total respiration. The respiration of intact cores of 800 mg CO2/m2 per h exceeded the previously obtained field average but was well within the range of maximum field values. Root respiration to root growth ratio measurements yielded an estimate of 33.9% root contribution to total soil respiration. A 30% root contribution to total soil respiration is proposed as a working estimate for tallgrass prairie with a well-developed root structure.