It was shown that among the factors determining the level of virus RNA infectivity considerable importance belonged to the time of RNA adsorption on cells, concentration and duration on treatment cells with NaCl.
   Rhysico-chemical properties of infectious RNA of VEE virus were determined. The virion RNA was found to sediment in sucrose gradient at 38-40 S. In fractionation of RNA in cesium sulphate density gradient RNA was found in one zone of 1,66 g/cm³ density.