The authors refered the previous publication of the results obtained when the influenza virus in saline suspensios of mice lungs was irradiated with small doses of X rays. The irradiated vírus was more virulent for mice than the control one. The effect of the exposition to 1 mg of radium was not significant. In the present paper the authors refered the experiments made with the poliomyelits virus, MEF1 strain, after exposition to 1 needle of 1 mg of radium and to 4 tubes of 1 mg of radium. The virus suspension was put into the Carrel flask in a fluid layer of 0,1 cm. The titulations of the irradiated virus suspension activity were made in the first case (exposition to the radium needle) after 7, 13, 20 and 30 days and, in other experiments, after 90, 120, 150 and 182 days of exposition. The results were not statistically significant. In the second case (exposition to the 4 tubes of 1 mg of radium each), after 60 and 90 days of exposition showed more activity than was shown in the control. After 127 and 139 days the control suspension completely lost the activity and the irradiated virus maintained the same infective title. In conclusion, the poliomyelitis virus, MEF1 strain, after radium exposition, in the described experimental conditions, showed higher infective title than the control. This property can be used to increase the virulence of that virus and, possibly of other viruses.