The Chemical weed control should apply herbicides which interfere only with the plant-specific processes, like photosynthesis, biosynthesis of pigments or essential amino acids. Accordingly, attention for herbicide development is focused on the chloroplast as a typical plant organelle. This páper reports on the mode of action of so-called bleaching compounds which affect the biosynthesis of carotenoids and chlorophylls, respectively, causing interrupted build-up or degradation of the photosynthetic apparatus. In the first čase such inhibitors lead to accumulation of precursors of P-carotene and xanthophylls, which cannot protéct chlorophyll (Chl) against the photooxidation. Herbicidal inhibitors of Chl biosynthesis result in accumulation of protoporphyrin IX which is sensitised by light thereby inducing radical peroxidative reactions. The peroxidative stress can - under certain circumstances - be counteracted by the antioxidative systém of the plant cell. Basic biochemical studies and molecular genetics in this field of herbicidal inhibitors research are briefly outlined.