A manual method for the extraction of inorganic mercury and the oxidation of organomercurials has been modified and incorporated into an automated procedure for the determination of mercury in sediments. The method includes a digestion of the wet sediment with sulfuric and nitric acids followed by oxidation of the organomercurials with potassium permanganate and potassium persulfate. Errors caused by coprecipitation and adsorption of mercury on manganese dioxide are avoided by reduction of the dioxide with a solution of hydroxyammonium sulfate and sodium chloride. The mercury content in solution is determined by a cold vapor technique with tin(II)sulfateas a reductant in an automated system. This method can detect down to 10 p.p.b. of mercury in sediment (based on 1-g samples) and can handle automatically 20 samples per h after manual digestion.