Adsorption characteristics of coliphages (host cell: E. coli B) to particulates (kaolin, sand, soil, microbial particulates in an oxidation pond) were investigated using batch experiments under various conditions of pH, concentrations of cations and concentrations of dissolved oxygen. The coliphages showed no resistance to acid (pH 3) and weak resistance to alkali (pH 10). Under neutral pH conditions, sodium ions did not have a large effect on the adsorption of coliphages to the solid surfaces of sand. Divalent cations (Mg++, Ca++) had no effect on the adsorption to sand at concentrations below 0.01 mol/l but some effect at 0.05 and 0.1 mol/l. The presence of kaolin had very little effect on removal of coliphages from the water phase under any conditions. Formation of floes such as Mg-hydroxides in alkaline conditions enhanced coliphage removal from the water phase. Coliphage chemical adsorption to particulates in natural waters would probably be low except in estuarine and sea waters. However, the adsorption of coliphages to microbial particulates occurred in aerobic conditions. The desorption of coliphages was observed under anaerobic conditions. This adsorption-desorption process was reversible. The biological adsorption appears to be the dominating cause of coliphage adsorption in natural waters containing microbial particulates.