Twelve tropical grasses (Digitaria decumbens (601), DigitariD decumbens (602), Digitaria milanjiana sub. sp. eylesiana, DigitariD pentzii (742), Digitaria pentzii (750), Digitaria setivalva, Digitaria smutsii, Digitaria umfolozi, Hemarthria altissima (993), Hemarthria altissima (995), Brachiaria sp., and Cynodon dactylon) established in small plots on River Estate soil were given a low, moderate or high level of nitrogen fertilizer (as sulphate of ammonia) ·equivalent to a rate of 224, 448 or 672 kg Nfhafyr, and cut mechanically at either a short (4 week) or long (8 week) interval of re-growth. Herbage D.M. yields varied significantly between grass species (P< 0.01), and within grasses D.M. yields were increased significantly (P L.. 0.01) by increasing nitrogen fertilization. At the 8 week harvest interval yields of herbage D.M. were significantly higher (P ~ 0.01) than at the 4 week harvest interval. The response in D.M. production by these grasses tended to diminish with increasing level of nitrogen fertilization. Herbage crude protein contents were higher in grasses cut at the short harvest interval, but increased with increasing nitrogen fertilization at both ages of harvesting. The results are discussed in relation to the optimum utilization of nitrogen fertilizer by improved grasses in the Caribbean.