The partial molar isentropic pressure coefficients at infinite dilution k(S,2)(infinity) = -(partial derivative V-2(infinity)/partial derivative p)s, where V-2(infinity) is the partial molar volume at infinite dilution, have been determined for six N-acetyl amino acid and peptide amides in aqueous solution at the temperature 298.15 K. The results obtained have been rationalized in terms of the likely solute - water interactions. The contribution of an alanyl side-chain to the value of k(S,2)(infinity) of a peptide has been derived. The result obtained is almost in agreement with that reported in previous work.