Process for dyeing hydrophobic fibre material from aqueous bath containing untreated disperse dye and to adjust the exhausted dye bath for further use

A process for dyeing hydrophobic fibre material with unformulated disperse dyes from an aqueous liquor containing a solubilizingly or dispersingly effective amount of surfactant or surfactant mixture having a hydrotropic action on disperse dyes, which process comprises dissolving one or more such dyes in water at a temperature of 50.degree. to 150.degree. C. by means of said surfactant or surfactant mixture, bringing the dye solution together with the substrate in a dyeing apparatus, then heating the dyeing liquor to the dyeing temperature, completing the dyeing at that temperature, then removing the substrate, restoring the exhausted dyeing liquor to the composition required for the next dyeing by adding water and surfactant in amounts corresponding to the amounts used in the previous dyeing and the same or different dye, and dyeing further substrate.