Methods and equipment are described for simultaneous measurements of heat flow rates, CO2 evolution rates, O-2 use rates and sample volumes for three samples in a differential heat conduction calorimeter. Isothermal measurements of metabolic heat rates were conducted in 1 ml sealed ampoules connected to pressure sensors. Pressure measurements in the presence and absence of a CO2 trapping solution allow determination of the gas flux rates. The decrease in the partial pressure of O-2 within the sealed ampoule under trapping conditions measures O-2 consumption by the tissue. The CO2 rates are determined by two methods. Absorption of CO2 produces heat at a rate proportional to the rate of CO2 production. Also, the difference between the rate of change of pressure with and without trapping solution yields the CO2 production rate by the tissue. Measuring gas flux by pressure change requires knowledge of headspace volume. Two methods of headspace volume determination are discussed. The first involves the introduction of a mass of known volume into the ampoule during pressure change measurements and the second involves recording the pressure increase upon addition of a known volume of gas into the ampoule. The methods described here are useful for studies of metabolic efficiency in biomass production and examination of responses of cell metabolism to changes in environmental or physiological conditions.