Abstract: A process for the thermal and chemical treatment of lignocellulose-containing biomass and for the production of furfural and cellulose-containing fiber masses. In order to ensure a high yield of furfural:lignocellulose-containing biomass is continuously fed into a cooker containing a cooking liquor and, upon heating of the biomass in a heating zone and guidance of the heated biomass through a consecutive retention zone, cellulose or pretreated biomass is continuously withdrawn from the cooker,cooking liquor is continuously withdrawn from the cooker,the cooking liquor withdrawn is continuously fed to a furfural production plant, andthe cooking liquor at least largely freed from pentoses and furfural is continuously returned to the cooker, wherein heating may be effected by direct steam or via the cooking liquor.