The present invention provides a process for the preparation of 4-hydroxy-3-(heterocyclocarbamoyl)-2H-1,2-benzothiazine-1,1-dioxides of the general formula: ##STR1## wherein R.sub.1 is a hydrogen atom or a methyl radical, R.sub.2 is a nitrogen-containing heterocyclic radical and R.sub.3 is a hydrogen or halogen atom or a methyl radical, and of the alkali metal, alkaline earth metal and amine salts thereof, by the reaction of an amine-substituted, nitrogen-containing heterocyclic compound with a halo-acetyl halide, reaction of the intermediate thus obtained with sodium benzoic acid sulphimide, ring expansion of the benzoisothiazole ring to give a benzothiazine ring and, in case R.sub.2 is to be an isoxazolyl radical, reverse rearrangement of the oxadiazole-ring formed by ring expansion to the isoxazolyl ring, wherein (in a one-pot reaction A) the reaction of an amine-substituted, nitrogen-containing heterocyclic compound with a halo-acetyl halide is carried out, without the addition of a base, in boiling ethyl acetate, the intermediate formed is, without isolation, reacted with sodium benzoic acid sulphimide and the reaction product isolated, whereafter, in a one-pot reaction B, the reaction product from the one-pot reaction A is reacted in a dipolar aprotonic solvent under an atmosphere of a protection gas with a strongly basic alkali-alkohole and thereafter with so much acid that about 2 equivalents of base remained unneutralized in the reaction solution and, if desired, the benzothiazine ring is N-methylated in the usual manner and the product obtained is, if desired, converted in known manner into an alkali metal, alkaline earth metal or amine salt.