Binding of MVL-2 virus, whose envelope lipids were radioactively labeled, to A. laidlawii JA1 cells was determined and characterized. The binding followed first-order kinetics and was temperature-dependent. All MVL-2 particles were capable of binding to A. laidlawii cells. At least 75 percent of radioactive MVL-2 bound represented specific binding which was markedly inhibited by EDTA. Virus infectivity was not essential for binding as inactivation of the virus by ultraviolet irradiation did not affect binding. Nevertheless, protein denaturing agents or proteolytic enzymes markedly inhibited MVL-2 binding, suggesting that the binding site of MVL-2 is of proteinaceous nature.