The in vitro gas production technique has been developed as a means of predicting the degradability of feeds. However, it was pointed out by Blümmel et al. (1997) that attention should be given to the other products of the incubation as well. Degraded feeds may be incorporated directly into microbial biomass, or they may be fermented to produce VFA and gas. One of the objectives of this experiment was to determine whether the proportion of degraded substrate that was partitioned to gas production varied with different feeds. Blümmel et al. (1997) observed a negative relationship between gas yield (ml gas produced/g substrate degraded) and microbial biomass yield (mg biomass/g substrate degraded) when poor quality forages were incubated. A second objective of this work was to determine whether this relationship was also observed when higher quality feeds were used.