Monoazo dyestuffs of the formula ##STR1## wherein R.sub.1 represents an aromatic radical, an aliphatic radical with 1-4 C atoms or a dialkylamino radical, in which the alkyl groups contain 1-C atoms, R.sub.2 represents hydrogen, halogen, alkyl with 1-C atoms, alkoxy with 1-4 C atoms or trifluoromethyl, R.sub.3 represents hydrogen, halogen, alkyl with 1-4 C atoms, alkoxy with 1-4 C atoms or trifluoromethyl and K represents the radical of a coupling component K-H of the formulae (II), (III) and (IV) ##STR2## wherein R.sub.4 represents alkyl with 1-4 C atoms or aryl,R.sub.5 represents hydrogen or unsubstituted alkyl with 1-4 C atoms,R.sub.6 represents hydrogen, nitrile, halogen, alkyl with 1-4 C atoms or alkoxy with 1-4 C atoms,R.sub.7 represents hydrogen, alkyl with 1-4 C atoms, aryl, a carboxylic acid ester group or a carboxylic acid amide group,R.sub.8 represents hydrogen, alkyl, cycloalkyl, aryl or the radical of a heterocyclic compound,R.sub.9 represents hydrogen, halogen, alkyl with 1-4 C atoms, alkoxy with 1-4 C atoms or acylamino,R.sub.10 represents hydrogen, halogen, alkyl with 1-4 C atoms, alkoxy with 1-4 C atoms or aryloxy,R.sub.11 represents hydrogen or alkyl,R.sub.12 represents hydrogen or alkyl and m represents 0 or 1,are suitable for the dyeing of synthetic fibre materials, especially those from polyamides. Level yellow, red and ruby shades are obtained with good dyeing yield and fastness.