The fiber-reactive formazan dyes of the formula ##STR1## in which n is the number 0, 1, 2 or 3, (R).sub.n is 0 to 3 substituents, independent of one another, from the group comprising halogen, C.sub.1-4 alkyl, C.sub.1-4 alkoxy, C.sub.2-4 alkanoylamino, hydroxyl, carboxyl and sulfo and Z is a radical of the formula ##STR2## in which R.sub.1 is C.sub.1-4 alkyl, R.sub.2 is C.sub.1-4 alkyl, which is substituted by hydroxyl, halogen, cyano, carboxyl, C.sub.1-4 alkoxy, hydroxy-C.sub.2-4 alkoxy, HO--(CH.sub.2 CH.sub.2 --O).sub.2-4 --, sulfo or sulfato, R.sub.3 is C.sub.1-4 alkyl, which can be substituted by hydroxyl, halogen, cyano, carboxyl, C.sub.1-4 alkoxy, hydroxy-C.sub.2-4 alkoxy, sulfo or sulfato, R.sub.4 is hydrogen, halogen, C.sub.1-4 alkyl, C.sub.1-4 alkoxy, carboxyl or sulfo, R.sub.5 is halogen, C.sub.1-4 alkyl or C.sub.1-4 alkoxy, m is the number 0, 1, 2 or 3 and (R6).sub.m is 0 to 3 substituents independent of one another, from the group comprising halogen, C.sub.1-4 alkyl, C.sub.1-4 alkoxy and carboxyl, and R.sub.4 in formula (1b) and the sulfo group in formula (1c) is bonded to the phenyl ring in the 4- or 5-position, are particularly suitable for dyeing or printing cellulose-containing fiber materials by the processes customary for reactive dyes and give, at a high dyeing yield, dyeings and prints of good fastness properties.