The adsorption to sediments and saturated soils of selected organic acid compounds was examined as a function of compound and sediment properties. Intrinsic compound properties examined included the dissociation constant (pKa) and hydrophobic character. Properties of the sediment examined included ionic strength and composition, organic carbon content and aqueous phase pH. By varying these properties, adsorption of both the neutral and anionic forms of these compounds was shown to occur. Adsorption of the neutral species occurs similarly to that of other hydrophobic compounds that do not contain acidic functional groups. Adsorption of the anionic species was influenced, however, by intrinsic chemical as well as electrostatic factors. Adsorption of the anionic species to a specific sediment was modeled as a linearly dependent function of pH. Compounds used in this study included 2,4-dinitro-o-cresol (DNOC), 2-(2,4,5-trichlorophenoxy)propanoic acid (silvex), pentachlorophenol (PCP), 4-chloro-α-(4-chlorophenyl)benzeneacetic acid (DDA) and 4-(2,4-dichlorophenoxy)butyric acid (2,4-DB).