The dynamic physiological processes of CO2 production, O2 uptake and ethylene synthesis for ripening tomato (Lycopersicon esculentum L.) and banana (M usa sp. cv `Valery') fruit were measured using a novel approach. Fruit were sealed in low density polyethylene pouches of known permeability to O2, CO2 and C2H4. The flux of these gases during the climacteric was closely tracked by their respective partial pressure in the headspace of the pouches. Some limitations in application exist due to modification of the atmosphere (primarily O2) within the pouch, however, the system provides some distinct advantages. These include the absence of gas handling equipment, measurement of O2 uptake despite high background levels of O2, measurement of the respiratory quotient, and measurement of low rates of ethylene production. Compared to low-flow, flow-through respirometers, this type of respirometer has the potential to permit the accumulation of several-fold higher levels of some gases due to the property of differential gas permeabilities possessed by polymer films.