Rates of carbon dioxide evolution from soil in mid—Missouri tallgrass prairie were highly correlated with temperature of the surface soil. Values increased exponentially with rising temperatures through the seasonal range under observation. Twenty—four—hour measurements employing infrared analysis were conducted periodically during all seasons from August 1968 to June 1970. Weekly averages calculated from regression for the entire year ranged from zero during the coldest period to 450 mg CO_2m(—2)hr(—1) during summer. The annual total was 1,675 g CO_2m(—2). The organic matter equivalent was 1,005 g, approximately 2.2 times the indicated biomass turnover for the root system for the same period. The difference was attributed to root respiration by determining a correlation between CO2 evolution and root biomass with KOH absorption and titration and by converting these data to infrared equivalents. It was estimated that 60% of the total respiration (surface litter excluded) was due to microbial processes in organic turnover and the balance to root metabolism.