Laboratory, digestion, and growth studies evaluated urea as a source of ammoniation for quality improvement in guineagrass (Panicum maximum) hay. Large round bales (320 kg) were reconstituted with water to yield a final moisture concentration of 25%, and treated with urea at 0, 4 or 6% of the forage DM. The urea solution was sprayed onto both flat surfaces of the bales. Each treatment was applied to three bales. Each bale was stored air-tight in individual 6-mil thickness plastic bags for 60 days. Crude protein concentration and in vitro organic matter digestion increased in a linear (P < 0.01) manner with increasing urea treatment level. Cell wall concentration decreased i n a linear (P < 0.05) manner with increasing urea treatment level, although the absolute reduction was minimal. In the digestion trial, six St. Croix While hair neutered male sheep (30 kg) were used in a replicated 3 X 3 Latin square design to evaluate the three urea treatment levels. In the growth trial, 30 sheep similar to those used in the digestion trial were allotted to six pens of five head each, with two pens assigned to the same three treatments. In the digestion and growth trials, hay intake increased in a quadratic (P < 0.05) manner with increasing urea treatment level. Apparent OM digestibility was not affected (P > 0.10), however apparent fiber digestibilities increased in a linear (P < 0.05) manner due to urea treatment. Linear improvements in daily gain (P < 0.05) and gain/ feed (P = 0.07) were observed by urea treatment. Urea ammoniation offers potential for improving the feeding value of tropical forages, and provides an option for quality forage during the dry season.