Agents and methods of using 4,6-(subst.)diamino-5-nitro-pyrimidines, most of which are new, which possess plant growth inhibiting, in particular herbicidal properties. The agents may also contain salts of the said pyrimidine derivatives. Preferably the 4,6-(subst.)diamino-5-nitro-pyrimidines are also substituted in the 2-position, especially by methyl, ethyl, methoxy or trihalomethyl.