Introducing enzymes during the extrusion process has been mainly used as new pretreatment techniques in the starch degradation process and, more recently, in the second generation bioethanol production. The technique, called the bioextrusion, is a special case of reactive extrusion. Starch and lignocellulose bioextrusion examples underline the good mixing capacities as a way to initiate the enzymatic reaction in high solid content conditions. Starch bioextrusion results show a low dextrinization yield but a real effect on the polymer size decrease which allows higher and faster subsequent saccharification. It also considerably reduced the recrystallization phenomenon that limits the saccharification efficiency. Bioextrusion of lignocellulose resulted in a better sugar production. Very short residence times limit the use of bioextrusion to a pretreatment technique. However, unique flexibility of the extrusion technique allows to subsequently pretreat, in the same extruder, with physical and/or chemical constraining conditions, followed by a milder bioextrusion.