Isotherms are reported for the adsorption of water vapor and benzo-15-crown-5 ether from aqueous solution onto one nonporous and three porous carbons. Specific adsorption of water at oxygen-containing sites on the porous carbons was followed by adsorptive aggregation of water molecules on the carbon surfaces and in pores. The adsorption of benzo-15-crown-5 ether was impeded by coadsorbed water and by the steric requirements of narrow pore entrances which denied the large molecules access to surface Within the carbon micropore structure.