The present invention relates to a process for the preparation of pure 3,3',4,4'-tetraaminobiphenyl in high yield by ammonolysis of 3,3,-dichlorobenzidine in the presence of copper powder and CuCl. After the crude product has been washed with ammonia water and water, the 3,3',4,4'-tetraaminobiphenyl, thus pretreated, is crystallized in water in the presence of 0 to 5% by weight of activated carbon and of about 1 to 2% by weight of a water-soluble reducing agent at temperatures of about 100.degree. to about 140.degree. C., under a protective gas atmosphere (redissolution). The water-soluble reducing agent is an alkali metal dithionite or alkali metal sulfite. The protective gas used can be nitrogen. The water used in the recrystallization (redissolution water) can be reused in whole or in part in the recrystallization.