Polysulfone ultrafiltration membranes were used to treat water from the Seine River--with and without coagulation pretreatment. Pretreatment with polyaluminum or ferric chloride coagulant reduced the rate of reversible fouling and increased the removal of dissolved organic carbon (DOC) but did not reduce the rate or extent of irreversible fouling of the membrane. Seine River water that had been treated by coagulation, filtration, and ozonation, i.e., tap water, also produced significant irreversible fouling. Most of the DOC in flocculated Seine River water and tap water consisted of polysaccharide materials of low molecular weight. Irreversible fouling may be due to the adsorption of these materials on membrane surfaces. Includes 23 references, table, figures.