Photoinduced nucleophilic substitution reactions of thirty p-nitrodiphenyl ethers including the herbicides nitrofen and chlornitrofen with a variety of amines were examined. The reaction took place by liberating nitrophenoxide or nitrite, depending on the substituents. Nitrofen liberated mainly nitrophenoxide by reactions with pyridine and 4- methylpyridine to give N-phenylpyridinums, whereas chlornitrofen liberated exclusively nitrite to afford N-phenyoxyphenylpyridinums. In organic solvents photoreduction of the nitro group occurred to form nitroso and azo compounds.