Reactive dyes of the formula I where a is 1 or 2, b is 0 or 1, Y is vinyl or a radical of the formula C2H4Q, where Q is an alkali-detachable group, Het is the radical of a 5- or 6-membered aromatic hetero-cyclic ring having from 1 to 3 hetero atoms selected from the group consisting of oxygen, sulfur and nitrogen, W is either in case 1) the radical of a coupling component, of a monoazo dye or additionally, when b=0, of a disazo dye, which may each bear further fiber-reactive groups, or in case 2) the radical of a chromophore which optionally has further fiber-reactive groups and is derived from an optionally metallized mono- or disazo dye, a triphendioxazine, an anthraquinone, a metallized formazan or a metallized phthalocyanine, and L1 and L2 are each a bridge member, are useful for dyeing or printing hydroxyl-containing or nitrogenous substrates.