Three isogenic lines of corn provided two levels of nitrogen for young men, but the diets were isonitrogenous at 5.5 g. Mean daily nitrogen balances were -0.28 +/- 0.34, +0.31 +/- 0.23 and 0.40 +/- 0.08 g, respectively, when normal, opaque-2 and sugary-2 opaque-2 corn furnished 5.5 g of nitrogen; and -0.07 +/- 0.17, +0.38 +/- 0.21 and -0.04 +/- 0.25 g when corn supplied only 4.4 g of nitrogen. Although these values were not significantly different, both high-lysine varieties tended to be superior to normal corn at 5.5 g of nitrogen and opaque-2 corn caused improvement even at 4.4 g of nitrogen. Lysine and tryptophan were higher and leucine lower in both opaque-2 and sugary-2 opaque-2 than in normal corn. Coefficients of apparent digestibility were between 65.5% and 68.8%.