The effect of various electrolytes on the adsorption of poliovirus was measured in 250-cm-long soil columns with ceramic samplers at different depths. Viruses suspended in deionized water moved much farther through the soil than those suspended in tap water, whereas movement in sewage water was intermediate. The salt content of the tap water and sewage water promoted virus adsorption, but evidently the organic compounds in sewage retarded adsorption. When viruses were suspended in chloride solutions of K, Na, Ca, and Mg, virus adsorption increased as the cation concentration and valence increased. The depth of virus penetration was related to the ionic strength of the solutions. Virus penetration data for NO(3), SO(4), and H(2)PO(4) salts of K, Na, and Ca indicated that other anions were more effective than Cl in promoting virus adsorption. Also, NH(4) was more effective than other cations in limiting the penetration depth of viruses. It seems that ions composed of radicals are more effective than ions composed of single atoms in promoting virus adsorption. Al was the most effective ion in limiting virus penetration, probably owing to flocculation of the viruses. Adding AlCl(3) concentrations to secondary sewage effluent to provide an Al concentration of 0.1 mM reduced the virus penetration depth to 40 cm. These studies show that the ionic composition of the suspending solutions must be considered in predicting virus penetration depths, and it may be practical to add low concentrations of a flocculating agent such as AlCl(3) to sewage water to limit virus movement through very porous soils.