Methane emission from free-ranging ruminants can be measured in different ways. In a study with 13 grazing dairy cows, Agroscope compared two methods. The sulfur hexafluoride (SF6) tracer technique is an established method, but its application is challenging and laborious. Before the measurements started, the cows were equipped with a calibrated permeation tube releasing SF6 in the forestomach. During the measurements, when the SF6 tracer technique and the GreenFeed (GF) system were applied simultaneously, daily individual respiration gas samples were collected through a flow-control capillary into evacuated canisters fixed on the cows' back and analyzed subsequently. The GF system is a mobile device measuring respiration gas output during voluntary visits of a feeding station. The aim of the study was to perform measurements with the GF system over five, seven and eleven days and to compare them with the measurements that were carried out in parallel with the SF6 technique over five days. The methane emissions estimated by GF were higher than those obtained using the SF6 technique. The correlation between methods was moderate and became hardly better when the measurement period with the GF was extended from five to eleven days.