High protein corn protein (HPCP) is a corn co-product derived from the ethanol industry that contains between 40 and 50% crude protein, and therefore, may be used in diets for pigs as a source of amino acids (AA). However, such diets will contain more than twice as much Leu as recommended and there is a negative relationship between dietary Leu and brain synthesis of serotonin, which results in reduced feed intake of pigs fed diets containing excess Leu. There is also a reduced protein synthesis because of increased Val and Ile metabolism due to excess dietary Leu. As a consequence, pigs often have reduced growth performance if fed diets with high concentrations of HPCP. However, it may be possible to counteract the negative effects of the high Leu concentrations in corn co-products by adding crystalline sources of Trp, Val, and Ile to the diets and it may, therefore, be possible that HPCP can be used in diets without influencing growth performance or intestinal health of weanling pigs. Therefore, the hypothesis that HPCP may be used as the primary source of AA in diets for weanling pigs if diets are fortified with crystalline AA was tested.