A field experiment was conducted near Barceloneta in the humid northern coastal plains of Puerto Rico to evaluate the production and persistence of 10 tropical grasses: Cynodon sp. local, Digitaria pentzii Slenderstem, C. nlemfuensis Star, C. plectostachyus Star, C. dactylon Coastcross-1, D. milanjiana Pangola Soto, Panicum maximum Guinea, P. maximum Guinea USDA PI 259553, P. maximum Makueni and D. decumbens Transvala grazed at 3- to 5-week intervals for one and a half year. P. maximum USDA PI 259553 was the most productive grass, but during the 13 grazings in 1981-1982, it was not significantly different (P=0.05) from C. plectostachyus Star; Cynodon sp. Local, D. pentzii Slenderstem, C. nlemfuensis Star, P. maximum Makueni, and D. decumbens Transvala. Guinea and D. milanjiana Pangola Soto were the least productive (P=0.05). Results for 7 grazings from January to June 1983 again showed P. maximum USDA PI 259553 to be the most productive grass, although not significantly different (P=0.05) from D. decumbens Transvala, C. dactylon Coastcross-1 and D. pentzii. The production of P. maximum Makueni and C. plectostachyus Star was intermediate; C. nlemfuensis Star and Guinea were the least productive, and D. milanjiana Pangola Soto did not persist under intensive grazing (P=0.05). The total mean production of all grasses of 0.92 and 1.00 ton/ha/grazing, respectively, were related to rainfall distribution. The general mean in crude protein content of forage was higher during the drier months. Average production of all grasses in this experiment was lower than in a similar experiment at Corozal in the humid region of Puerto Rico, the relative difference varied among cultivars.