The dilution enthalpies of glycine and L-alanine in aqueous I-propanol solutions have been measured by a mixing-flow microcalorimeter at T = 298.15 K. The homogeneous enthalpic interaction coefficients of the two zwitterions have been calculated according to the analysis of the excess enthalpy suggested by Friedman [J. Solution Chem. 1 (1972) 387-390]. The enthalpic pairwise interaction coefficients h(2) of glycine are negative and pass through a minimum with increasing 1-propanol content in mixed solvents, while those of L-alanine decrease from positive to negative. The variations of the enthalpic pairwise interaction coefficients are interpreted in terms of solute - solute and solute - solvent interactions. (c) 2004 Elsevier Ltd. All rights reserved.