Protein changes were evaluated in two different maize genotypes of contrasting protein quality made into tortillas. In both types of maize, albumins, globulins, zeins, and glutelinlike components became insoluble after interacting with other biochemical entities catalyzed by the alkaline pH and the heat produced in tortilla-making. Increased nitrogen recovery with solvents having alkaline pH, a reducing agent, and sodium dodecyl sulfate indicate that hydrophobic interactions may have been involved in this change in solubility of proteins that are more easily solubilized in the unprocessed maize grain. In vitro protein digestibility with pepsin declined as nitrogen content increased in the glutelin fraction and in the residue after fractionation. Tortillas made from quality protein maize (QPM) had a superior amino acid score mainly because of their very high lysine and tryptophan content, which was not significantly affected during tortilla preparation. The superiority of the product obtained with the QPM sample was demonstrated by its high content of available lysine. Although the in sulfate indicate that hydrophobic interactions may have been involved in vitro digestibility of protein with pepsin and the amount of available lysine this change in solubility of proteins that are more easily solubilized in the changed during tortilla-making, no evidence was found of a specific unprocessed maize grain. In vitro protein digestibility with pepsin declined detrimental effect on the protein quality of the original QPM grain.