Abstract : An investigation was initiated to screen variola virus. The experimental data are concerned with methods of assaying the virus quantitatively, determining optimal conditions for culture growth, and the effect of various physical and chemical reagents on its viability. Viability after lyophilization and the storage stabilities of both liquid and dried organisms were noted. Monkeys, as a test host, were infected by the parenteral, oral, intranasal, and aerosol routes. The disease picture in these animals was similar to that of human infections. The findings of viral cytopathogenicity and propagation of the organisms in different tissue cultures are given.