Abstract: As a part of a series of studies on the complex formation of organic acids with amino acids, the heats of reaction (H) for formation of solid complexes of glycine with oxalic acid, maleic acid, malonic acid, glutaric acid and aminomalonic acid were determined. The values for H, were found 1-5 kcal/mol from the measurements of the heats of solution of the solid complexes and their components. The correlation of heats of reaction with the PKa values of the organic acids was discussed.