The invention relates to azo dyes having general formula (I), wherein one of radicals X?1 and X2¿ represents hydroxy and the other represents amino or C¿1?-C4-alkylamino optionally substituted by hydroxy, cyano, carboxyl, hydroxysulfonyl, methoxycarbonyl, ethoxycarbonyl or acetoxy; n equals 0 or 1; m equals 1 or 2; k equals 0 or additionally 1, 2, 3 or 4 when X?3¿ stands for NH¿2?; D?1, D2, D3 and D4¿ independently represent hydrogen or hydroxysulfonyl; Z1 represents a direct bond or a binding link of formula SO¿2?NH-A, -SO2Nalk-A, -SO3-A-, NH-A-, Nalk-A-, -SO2-A-, SONH-A-, or CO-A, wherein A represents phenylene which may be substituted by hydroxysulfonyl or carboxyl, or naphthylene which may be substituted by hydroxysulfonyl or carboxyl, whereby A is bonded to the azo bridge; Alk represents C1-C8-alkyl which may be interrupted by 1 to 3 non-adjacent oxygen atoms, 1 sulfur atom or 1 sulfonyl group and may be substituted by hydroxy, C1-C4-alkanoyloxy, benzoyloxy, halogen, cyano, carboxy, hydroxysulfonyl, carbamoyl, phenyl or hydroxysulfonylphenyl or C5-C8-cycloalkyl; K represents the radical of an optionally substituted derivative of a benzol, naphthalene, pyrazole, pyridine, pyrimidine, indole or N-arylacetoacetamide series; X?3¿ represents hydrogen or amino and Y represents a radical -CH¿2?CH2OH, -CH2CH2-ND?5D6¿, -CH=CH¿2? or -CH2CH2Q, wherein Q represents a group that may be separated under alkaline reaction conditions. The invention further relates to the mixtures of said dyes, to a method for their production and to their use for dying natural or synthetic substrates.