A process for producing fibrous material which includes the following: preparing a solution of chemicals that includes less than 25% of sulphite (calculated as Na2SO3), based on the oven-dry amount of the lignocellulosic raw material; mixing the solution of chemicals with wood in a specified liquor material; heating the solution of chemicals and the wood to a temperature above room temperature; and then either of the following alternatives: (1) removing the free-flowing solution of chemicals and digestion of the wood in the vapor phase; (2) having the wood digested in the liquid phase and separating the free-flowing solution of chemicals and the wood.