AbstractCertain ethylenes and heterocyclic compounds substituted with the 2,4‐dinitrophenylthio‐ group were synthesised and tested for activity againstVenturia inaequalis, Botrytis cinerea, Fusarium bulbigenumandCercospora melonis.1‐Alkylthio‐1‐(2,4‐dinitrophenylthio)‐2‐cyano‐2‐(ethoxycarbonyl or cyano) ethylenes in which the Ph‐S bond is not shielded by the alkyl substituent from attack, perhaps by nucleophilic cell constituents, were found to be active againstVenturia.3,5‐Di(methyl‐ or ethyl‐thio)‐4‐cyanoisothiazoles were also active againstVenturia.2‐Substituted‐5‐(2,4‐dinitrophenylthio)‐1,3,4‐oxadiazoles had no or low fungicidal activity, and of several 2‐(2,4‐dinitrophenylthio) heterocyclic compounds that were tested 2‐(2,4‐dinitrophenylthio)‐benzothiazole and ‐benzoxazole had good activity againstVenturia.The infra‐red and proton magn