Encephalomyocarditis viruses adsorb to introduced organic and inorganic solids in water over a wide range of pH and with various concentrations and species of metal cations. Visible flocculation of solids was not a prerequisite for significant virus association. Virus adsorption to natural solids in various types of natural waters was significant but variable. Clay-adsorbed virus retained its infectivity in tissue culture monolayers. These solids-associated viruses also retained infectivity in mice. Various enteric viruses are excreted in human feces and urine during infection and may be found in raw domestic sewage. Excellent reviews such as those prepared by Grabow (13) and Berger et al. (2) provide ample evidence that the use of secondary treatment processes such as trickling filtration, activated sludge, and oxidation ponds can reduce the infectious virus titers by varying degrees. The removal of infectious viruses by these processes is not complete, however, and each process appears to give variable results. Even chlorination of the secondary effluents may not disinfect the waste waters. This effluent discharged into receiving waters often introduces enteric viruses to those waters. Infectious viruses can be carried in the natural resource to points distant from their origin in sewage. Reports indicate that it is not uncommon for fresh and estuarine waters to carry detectable virus several miles (14,