The osmotic coefficients of aqueous solutions of the am-amino acids: 3-aminopropanoic acid, 4-aminobutanoic acid, 5-aminopentanoic acid and 6-aminohexanoic acid were measured using the isopiestic method at 298.15 K. The activity coefficients of these solutes were calculated from the experimental osmotic coefficients and the pairwise free energy coefficients for solute-solute interactions were obtained using the Mc-Millan-Mayer theory. The results are compared with the activity coefficients of a-amino acids and are discussed in terms of solute-solute interactions. (C) 2014 Elsevier B.V. All rights reserved.