The invention relates to a process for the dyeing and printing of polyester material in a weakly acid, neutral or alkaline solution of at least one altered dispersion dyestuff water-soluble at an intermediate stage and containing a carbacyl group which is bound by way of an oxygen atom, and which can be split off under the dyeing conditions, the said carbacyl group carrying at least one sulphonic acid or carboxylic acid group, to a process for the production of these dyestuffs water-soluble at an intermediate stage, as well as to new water-soluble dyestuffs. Compared with the conventional process of dispersion dyeing, this process offers certain definite advantages, namely, the dyestuffs need not be present as a dispersion, the complicated milling problems associated with dispersion dyestuffs are eliminated; no dispersing agents are required, which are mostly toxic and thus burden the effluent; and hence, furthermore, the troublesome foam problems normally occurring in large-scale dyeing plants are likewise avoided.