An improved process for the preparation of azo dyestuffs of the formula ##STR1## comprising diazotizing a 2-halo-4-nitroaniline at 10.degree. to 35.degree. C. in 70 to 100 percent by weight strength acetic acid by means of nitrosylsulphuric acid, adjusting the acetic acid content of the resulting diazo solution to 60 to 85% by the addition of water, and at a temperature from 15.degree. to 45.degree. C. adding an appropriate carbazole to the diazo solution as a solid or in the form of a suspension in 60 to 100 percent strength by weight acetic acid and coupling the carbazole to the diazotized amine to produce said azo dyestuff and isolating the dyestuff.