Abstract: An apparatus for carrying out biochemical reactions in microtiter plates includes a device (42, 43) for receiving and holding microtiter plate (44) to be processed, the microtiter plate being provided with a plurality of wells and each well having a bottom outlet, and a movably mounted device (47) for the application of gas pressure to the wells of the microtiter plate (44), the pressure device including a sealing collar (48) and being movable between a position where it leaves the upper part of the microtiter plate accessible, and a position where it sealingly contacts the microtiter plate through the sealing collar (48) so that a gas pressure may be applied to the inlets of the microtiter plate wells for pressing out liquid present therein through the bottom outlet of each well.