The methane emission from the digestive tract of cattle in Denmark accounts for 45% of the total methane emission based on the assumption that 6% of the gross energy is metabolized to methane. There is a lack of newer experimental data available for Danish cattle; therefore we have built a unit for quantitative measurements of methane, based on the principles for an open circuit system for indirect calorimetry. The chambers are transparent (polycarbonate) and open in the bottom, the inlet air is coming from the barn, and air-condition is a simple radiator to cool and condense for dehumidifying the chamber air. The system constitutes of four chambers, flow meters and gas sensors for measuring methane, oxygen and carbon dioxide. The outside measurements of chambers are approximately 1.45 * 3.9 * 2.45 meters. Inside there is a platform to give the cows a comfortable laying area, space for feeding bin, water bowl and draining of urine and faeces. The air flow out of the chambers can be controlled individually by a motor controller. The outlet is in the top of the chambers through a filter box to reduce the dust content before the flow meter (Teledyne Hastings, delivered by Columbus instruments, Ohio, USA), which can measure flow rates up to 3000 standard liters per minute. After the air has passed the flow meter an air sample is drawn. A manifold, drying system, oxygen sensor, carbon dioxide sensor, methane sensor, and data program for management were delivered by Columbus instruments (Ohio, USA). Methane and carbon dioxide are measured by infra red sensors and oxygen by a paramagnetic sensor. The system has five channels; one for each chamber and one for measuring the background in the barn. Each measuring cycle take twelve and half minute, flushing two minutes and measuring a half minute. The recoveries of methane and carbon dioxide have been checked and found to be 100% ± 10% (min-max). As chambers are placed in the barn the background level vary and need to be considered. The system has been working for four months and although we still work on improving the system, it seems to fulfill our expectations for a system for exact measurements of methane emission in dairy cows at production level under close to natural in barn conditions, where cows’ behavior can be expected to be natural.