A method is shown for estimating the degree of hydrophobicity of polymeric adsorbents and active carbons. The method is based on measuring the adsorption equilibirium constant K of three or more organic acids in a homological series, e.g. butyric (n = 4), valeric (5) and capronic (6) acids, and relating the constants K to the methylen group number n. Results are compared with those of earlier calorimetic measurements and yielded in the same sequence of adsorbents.