The in situ measurement of rumen degradability explains properly the disappearance of rumen feeds by solubilization. However, this methodology does not assure wheather the material in the rumen indeed suffered microbial degradation, or if the loss of material occurred by other reasons. The in vitro gas production technique, on other hand, measures a product of the fermentation process. If the remains of the gas production is recovered at pre-determined intervals, we could also determine the rate and extent of the degradation occurred in the process. Thus, the aim of this work was to compare the rate and extent of the degradation obtained from these two methodologies.