The invention relates to a method for activating a polysaccharide by bringing the polysaccharide into contact with liquid ammonia. According to said method, the polysaccharide is brought into contact with the liquid ammonia in the presence of an inclusion agent which is soluble or dispersible in liquid ammonia and the volume available to the polysaccharide/inclusion agent/liquid ammonia system is increased explosively by reducing the pressure by at least 5 bar. Urea cannot be used as the inclusion agent if the polysaccharide is cellulose. The product of the method retains a high level of activation, remains highly accessible to reagents and remains highly reactive for a long time without a residual quantity of ammonia which would be undesirable for subsequent applications being necessary or without the residual quantity of ammonia having to be subsequently replaced with an inclusion agent.
