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Previous experiments have shown that when the crude protein of a growing diet is reduced from 16 to 11% there is reduced growth performance of pigs, even though the diets are supplemented with lysine, tryptophan, threonine, and methionine. To determine which amino acid was next limiting in a corn-soybean meal, low-protein (11%), amino acid-supplemented diet, we conducted three experiments. In each of the three experiments, 36 growing gilts were individually penned and fed one of six diets. The three first diets were used in all three experiments: 1) 16% crude protein (CP) positive control, 2) 12% CP neutral control, and 3) 11% CP negative control. In Experiment 1, the 11% CP diet was supplemented with: 4) isoleucine, 5) valine, and 6) isoleucine + valine. In Experiment 2, the 11% CP diet was supplemented with: 4) histidine, 5) histidine + valine, and 6) histidine + valine + isoleucine. In Experiment 3, the 11% CP diet was supplemented with: 4) valine, 5) valine + histidine, and 6) valine + isoleucine. All low-protein diets were supplemented with lysine, tryptophan, threonine, and methionine. The supplementation of isoleucine or histidine alone reduced feed intake, daily gain, feed/gain, daily lean gain, longissimus muscle area, and backfat thickness. Valine supplementation improved growth performance, but the combination of valine with isoleucine or histidine increased growth performance to levels similar to those of gilts fed the 16% CP diet. Plasma urea nitrogen decreased as the crude protein decreased from 16 to 11%. These results suggest that dietary crude protein can be reduced from 16 to 11% with little or no effect on pig performance if amino acids such as valine and isoleucine or valine and histidine are added. This reduction in dietary crude protein will reduce nitrogen excretion in feces and urine.