One hundred and one tropical grasses, lightly fertilized with ammonium nitrate at the rate of 350 kg/ha, were harvested by hand (machete) at 30 days of growth. Crude protein content ranged from 9.8 to 23.8% while lignin content ranged from 2.6 to 7.9%. Wide ranges in the percentage of neutral-detergent fiber (45.7 to 79.2%), acid-detergent fiber (30.9 to 45.3%), hemicellulose (11.7 to 37.5%), and silica (0.4 to 5.5%) were obtained. Digestibility estimates obtained by the Tilley and Terry method and neutral-detergent fiber digestibilities had wide ranges: 42.6 to 66.0% and 22.0 to 62.0%, respectively. Total dry matter disappearance ranged from 44.3 to 78.2%. Digestibility estimates from predictive equations ranged from 74.0 to 94.5% for estimated digestible dry matter, 67.3 to 91.7% for estimated true digestible dry matter, and 54.4 to 78.8% for estimated apparent digestible dry matter. Analysis of variance showed significant variations between and within genera, indicating a possibility of genetic improvement through selection for high nutritive value. Silica was variably correlated with digestibility depending on genera. Acid-detergent fiber seemed more important than lignin in determining digestibility values. The significance of the term L/ADF in relation to digestibility estimates among all data and among genera was much less for in vitro estimates than for estimates calculated from predictive equations. This may indicate that lignification of cellulose has less influence on digestibility of tropical than of temperate forages. The estimated digestibility values based on fibrous constituents were poorly correlated to in vitro digestibility values, indicating inadequacy of using predictive equations developed for temperate forages with tropical grasses. Correlation coefficients between measured parameters showed great variation among four genera: Paspalum, Pennisetum, Digitaria, and Panicum.