A field experiment was conducted on a private farm near Toa Baja in the humid northern coastal plains of Puerto Rico to evaluate the production and persistence of 12 tropical grasses, Cynodon nlemfuensis var. nlemfuensis Star, C. dactylon Coastcross-1, Brachiaria brizantha Signal, B. ruzuziensis Congo PR PI 5366 and 11716, C. dactylon Toño, Eriochloa polystachya Carib, C. plectostachyus Star, Digitaria decumbens Transvala, C. plectostachyus Star, B. radicans Tanner and Panicum maximum Makueni under grazing at 3- to 5-week intervals for 2 years. Average production per grazing period, 1.59 and 1.52 ton/ha, respectively, was not significantly different (P = 0.05) among species and cultivars in either year. Forage production in December and May was low compared to that of other periods. This difference might have been associated with low rainfall in December 1983 and April 1984. Lower production in October and early November, 1984, was due to unusually low rainfall that year. Differences in relative palatability of the large number of species and cultivars, and the low grazing pressure at which they were evaluated might explain the lack of significant differences in the performance of these grasses. These variables must be taken into consideration in the design of future experiments for better interpretation of the results.