The standard molar enthalpies of solution at infinite dilution Delta(sol)H(m)(infinity) of N-acetylglycinamide, N-acetyl-L-alaninamide, N-acetyl-N’-methylglycinamide, and N-acetyl-N’-methyl-L-alaninamide in aqueous solutions of sodium chloride, potassium chloride, and sodium iodide have been determined by calorimetry. The results obtained were used to calculate the heterotactic enthalpic interaction coefficients h(xy) and h(xyy) of peptides with the three salts. The effects of the ion type, of the structure of the amino acid chain, and of methylation of the acid amide group on the magnitude and sign of the enthalpic interaction coefficients are discussed.