As a result of the "Large-Scale Combustion Regulations" which came into force in August 1989 about two million tonnes of desulphogypsum are produced in the Federal Republic of Germany in the wet desulphurization process used in coal-fired power stations. The desulphogypsum produced is not a waste product but a marketable high-grade raw material, so individual gypsum producers have looked for possible ways of using this desulphogypsum for which they have developed various processes. A report is given of a method for calcining natural gypsum and desulphogypsum to produce hemihydrate plaster in a new plant specially erected for this purpose in 1990, and of the operating experience obtained so far.