An ever-present problem in the use of commercial membranes for treatment of drinking water is fouling of the membranes by natural organic matter (NOM). This work describes a new approach to elimination or minimization of membrane fouling by NOM. When a 2% solution of polysulfone in NMP and propionic acid is slowly injected into water, similar to 50 nm polysulfone particles are spontaneously formed, and these hydrophobic particles quickly coagulate into similar to 12-mu m diameter aggregates; the formed material has a surface area of similar to 100 m(2)/g and an equivalent "pore" size of 25 nm. When 50 mg/L of the new material is equilibrated with a local drinking water supply, virtually all adsorptive fouling of a 20-kDa molecular weight cutoff ultrafiltration membrane is eliminated. Interestingly, although only a very small percentage of the NOM is removed by adsorption on the polysulfone aggregates, it appears that exactly this small NOM component is responsible for nearly all of the membrane fouling. This paper describes the fabrication and characterization of the new polysulfone adsorbent and offers an hypothesis for the formation of the product via spontaneous emulsification and spinodal decomposition.