A dyestuff of the formula ##STR1## wherein A=H, unsubstituted C.sub.1 -C.sub.4, C.sub.1 -C.sub.4 -alkyl substituted by OH, SO.sub.3 H or COOH or phenyl or COOR',R'=H or C.sub.1 -C.sub.4 -alkyl,X=--CH.dbd.CH.sub.2 or --CH.sub.2 C.sub.2 --Y,Y=--OSO.sub.3 H, --SSO.sub.3 H, --OCOCH.sub.3 or Cl,R=H, unsubstituted C.sub.1 -C.sub.4 -alkyl, or C.sub.1 -C.sub.4 alkyl substituted by OH, SO.sub.3 H, COOH, or OSO.sub.3 H or NR"Z, whereinR".dbd.H, unsubstituted C.sub.1 -C.sub.4 -alkyl or C.sub.1 -C.sub.4 -alkyl substituted by a substituent selected from the group consisting of OH, SO.sub.3 H, COOH, OSO.sub.3 H, and Z=a heterocyclic fiber reactive radical selected from the group consisting of 2,4-dichlorotriazin-6-yl, monohalogeno-sym.-triazinyl, monohalogenopyrimidinyl, dihalogenopyrimidinyl and trihalogenopyrimidinyl. Such dyestuff gives, on cellulose or polypeptide materials, high yields of brilliant yellow dyeings with outstanding wet--and oxidation--fastnesses and a high stability of the fiber--dyestuff bond.