The invention describes a process for the HT dyeing of polyester fibre material with dyes which are sparingly soluble in water, which process comprises the use of a dyebath which contains at least one block polymer of ethylene oxide and propylene oxide having a molecular weight higher than 5000.The use of such a polymeric non-ionic dispersant ensures, even in low concentration, the stability of the dye dispersion under HT conditions, with at the same time substantial to complete bath exhaustion.