Adsorption equilibria at about 1000 atm were measured for aqueous solutions of aromatic compounds. No significant difference between the isotherms at atmospheric pressure and at 1000 atm was found for nitrobenzene and ethylbenzene on activated carbon fiber. The decrease in the amount adsorbed due to the solubility increase with pressure and the increase in the amount adsorbed caused by compression of the adsorbed phase were considered to cancel each other. On the other hand, pressure had a marked effect on the adsorption of L-phenylalanine on a macroreticular adsorbent, resulting in a 1.5 to 2 times larger amount adsorbed at 1500 atm. The pressure effect was greater with larger amounts adsorbed. This implies that the molar volume of the adsorbed state is smaller than those of the pure state and dissolved state, and varies with the amount adsorbed.