1‐(2′,4′‐dichloro)phenylamino‐1H‐pyrrole‐2,5‐dione and 1‐(2′,4′,6′‐trichloro)phenylamino‐1H‐pyrrole‐2,5‐dione were prepared via direct chlorination of 2‐phenyl‐3‐oxo‐6‐hydroxy‐2H‐pyridazine. Both pmr and mass spectroscopy clearly showed that dichloro substitution occurred in the aromatic moiety and not in the vinylic region of the molecule. The former method showed that pyridiazine‐ to pyrrole‐ring isomerization had occurred already at the level of dichlorination. The identical 2′,4′‐dichlorophenyl and 2′,4′,6′‐trichlorophenylpyr‐rolediones were also prepared by reaction of maleic anhydride with the appropriate arylhydrazine. Similar 2′,4‐dichlorophenyl and 2′,4′,6′‐trichlorophenyl analogues were prepared using dichloromaleic anhydride. Cmr spectroscopic techniques were used for pyridazine‐/pyrrole‐ring stereochemical assignment of products derived from dichloromaleic anhydride. 1‐(2′,4′‐dichloro)phenylamino‐1H‐pyrrole‐2,5‐dione and the trichloro‐phenyl analogue were shown to exhibit fungicidal activity in both in‐vivo and in‐vitro assays.