During the dry season months from June to August, 56 randomly selected female Junin breed sheep at the IVITA-El Mantaro Research Station, Huancayo, Peru, were fed during 21 days four different diets designed to determine the effect of bypass protein (fish meal) on weight gain in sheep fed urea treated crop residues (barley straw with amonia). The four diets were comprised of: 1) 230 g of cotton cake, 2) 161 g of cotton cake and 42 g of fish mea], 3) 69 g of cotton cake and 97 g of fish meal and 4) 140 g of fish meal. Each diet supplied approximately 72 g protein per animal. Additionally ali the animals received 200 g of alfalfa hay and had free access to water and barley straw treated with amonia. Daily weight gains were recorded, and ali four diets produced similar (p>0.05) results: 1) 240, 2) 265, 3) 276 and 4) 255 g/day. The results indicate, that under conditions of the present experiment, the addition of bypass protein to a diet including amonia treated straw fails to produce additional weight gain in sheep.