A red clover-grass mixture and a couch grass (E. repens) pure stand were studied at eighteen different stages of maturity in Viikki. The analytical techniques were a cellulase digestion method and a two stage in vitro digestion technique. A high correlation (r = .99*** for both types of stand and residual standard deviations (RSD) of 0.9 and 1.3 respectively) was found between cellulase DM digestibility and in vitro DM digestibility. The difference between cellulase and in vitro DM digestibility increased as the plants advanced in maturity, because the effect of enzyme decreased, as the plants were more matured. The relationship between cellulase DM digestibility and plant protein content was very close, (r = .99***for the clover-grass mixture and couch grass and RSD’s of 0.6 and 0.5 respectively). At the early stages of maturity when the plant protein content and in vitro DM digestibility were high, the cellulase technique digested more efficiently the clover-grass mixture than the couch grass. The cellulase method was rapid, reproduciple and well suited to the evaluation of the plant material studied.