Abstract: In a process for dyeing textile material including polyester fibers, the textile material is treated in an alkaline dye bath containing a dispersion dyestuff at a temperature above 100.degree. C. The pH-value of the dye bath is adjusted by the initial addition of a buffer mixture preferably comprising glycine and soda lye prior to the commencement of the dyeing operation. A perborate salt such as sodium perborate is also added. The pH-value is kept substantially constant from the beginning to the end of the dyeing operation. A sequestering agent including nitrilotriacetic acid and polycarboxylates can be alternatively or additionally added to the dye bath.