The amino acid concentration in the protein of batches of corn kernel subjected to infestation by P. truncatus, S. zeamais or S. cerealella was measured. For each insect species three development stages were studied, larvae, at the emergence of the first generation, and longer. Differences between the control and each of the nine infested batches were observed for most of the amino acids. The only pattern of differences consistent in magnitude, significance and sign, was a fall in leucine and isoleucine and a raise in tryptophan concentration. The chemical scores of all samples were similar to the control, except in the case of infestation by larvae of S. cerealella in which it decreased 15%.