A simple mini-butane burner or "artificial rat," for calibration of small animal indirect calorimeters (modified Benedict and Haldane systems), was developed. Substitution of this burner for a live animal at regular intervals in an experimental protocol provides a means by which whole system function can be verified without disturbing respirometer conditions. Heat production, degree of total combustion of butane, proportion of unburned butane, and the CO2 production (VCO2)-to-O2 consumption (VO2) ratio were determined in animal and burner experiments by direct measurement or were derived from mass equations. Burner security was also discussed. VCO2/VO2 obtained in calibration experiments using the Benedict system remained constant and was not significantly different from the expected value for total combustion of butane. Observation of a stabilization phase in the Haldane burner experiments illustrated the utility of calibration over the duration of a normal animal experiment. This miniburner gave highly reproducible results and simulated the daily VO2, VCO2, and heat production of an adult rat.