AbstractSome symmetrical and unsymmetrical 2, 3‐bis(arylthio)‐1, 4‐naphthoquinones have been synthesised and assayed against Botrytis cinerea, Cladosporium fulvum and Venturia inaequalis. With the surprising exception of the 2, 3‐bis(4‐chlorophenylthio) derivative, the compounds were essentially inactive. The 2‐phenylthio and lower 2‐alkylthio derivatives showed a high level of activity, which was absent in the 2‐pentylthio and hi