Since automated gas production equipment became available (Cone et al., 1996), there is an increasing interest in this technique. The gas production technique is not only widely used in reasearch programms, but is also used as a routine feed evaluation technique and will soon be used in feed evaluation systems, as the gas production technique potentially can replace the nylon bag technique. Although many investigators use the technique, the interpretation of the gas production profiles is still difficult (Cone et al., 1997). The gas production caused by the fermentation of carbon hydrates is well understood and described (Beuvink and Spoelstra, 1992). Since, the gas production caused by fermentation of protein is not the same as that of carbon hydrates, comparing the gas production data of feedstuffs, differing largely in protein content, may lead to misinterpretation of the results. The aim of this study was to investigate the influence of protein fermentation of gas production profiles.