Summary.The herbicidal activity of substituted benzonitriles was determined by a number of tests. This activity was compared with the structure of the molecules. It was found experimentally that benzonitriles, substituted at the 2 and 6 positions by halogen or methyl, had the highest activity. Some 2,6‐dichloro‐1‐substituted benzene derivatives showed a herbicidal activity, comparable with that of 2,6‐dichlorobenzonilrile. These compounds possessed a group which could be converted into a nitrilc group.La relation entre la structure ft l'activité herbicide des benzonitril‐es