Abstract Correlations between in vitro dry matter (DM) digestibility and amount of DM dissolved in acid pepsin and cellulase enzymes for 24 tropical forage samples gave a value of 0.91 but a high sample standard deviation of 6.50 and a coefficient of variation of 25 %. This suggests that the cellulase technique requires further study if it were to be used as a predictor of rumen liquor in vitro digestibility values for tropical grasses and legumes. An improved correlation of r = 0.98 with sample standard deviation of 2.29 was obtained when percent DM dissolved in acid‐pepsin and cellulase enzymes was compared with the in vivo dry matter digestibility values of 11 tropical forage grasses and legumes. This result suggests that the pepsin‐cellulase technique may be used to predict in vivo DM digestibility values in tropical grasses and legumes.