A reverse-phase high-performance liquid chromatography procedure with gradient elution and electrochemical detection is described for the determination of phenolic compounds, including several priority pollutant chlorophenols, in sea-water and sediments. In addition, a method for concentrating phenols from sea-water was examined. A solid-phase extraction using a derivatized poly(styrene-divinylbenzene) copolymer is discussed. The recovery, repeatability and detection limits are shown. Electrochemical detection provided selectivity as well as sensitivity. Phenols at the ng/l level were detected. The method was applied to the analysis of the most important phenolic compounds in sea-water and marine sediments.