A Reactor (1) for solid phase synthesis comprises a vessel (2), a plurality of filters (3) arranged in the vessel (2) and a plurality of filtrate outlets (4) for evacuating the filtrate out of the filters (3). Each filter (3) is connected to one filtrate outlet (4). The reactor (1) comprises means (3, 4) for delivering a gas into the vessel (2) in a region of the vessel (2) near to the bottom (24) of the vessel (2) and beside the filters (3).