5-Amino-o-nitrobenzimidazol-2-one, very convenient as educt for azo pigments, was diazotized and coupled with acetylacetic acid and 3-hydroxynaphthoic acid arylides and also with 1-phenyl-3-methyl-5-pyrazolone to yield 8 pigments. These heated 3-5 h in N,N-dimethylformamide or methoxy-dipropenyl glycol at 120 and 140-150degreesC, resp., recrystd. to yield dimerized pigments more intense in color, more resistant to temp. (350degreesC) and org. solvents (EtOH, AcOEt), more light-fast, and enhanced in texture.