Abstract Methyl, ethyl and isopropyl methanesulfonates (MMS, EMS, iPMS), diethyl pyrocarbonate (DEP) and autoclaved irradiated sucrose and glucose (active principles presumably α,β-unsaturated carbonyl compounds) inactivated the transfectivity of Q β RNA in one-hit processes. In the case of DEP, nealy every carbethoxy group introduced inactivated, whereas several alkyls from the methanesulfonates per RNA molecule seemed te be tolerated. 1,2-Dibromoethane was a relatively strong inhibitor of RNA transfectivity in the presence of thioglycol, probably via the formation of a more reactive “half mustard”. Compared with isolated RNA, the complete Q β phage was somewhat protected against methanesulfonates but slightly more sensitive to the irradiated sugars and distinctly more sensitive to DEP, indicating that the two latter compounds may inactivate in reactions with coat proteins. The negative tests with the strongly mutagenic 2,3,7,8-tetrachlorodibenzdioxin suggest that intercalating agents are probably not active towards RNA. The decrease of the trasnfectivity of Q β RNA may be used as a sensitive system to determine reactivity towards nucleic acids of environmental pollutants.