The cartridge according to the invention for analysing biological samples comprises: a reaction chamber and a biochip mounted in the reaction chamber, a filling nozzle connected so as to communicate with the reaction chamber, and a compensation chamber connected so as to communicate with the reaction chamber, wherein the reaction chamber, the compensation chamber and all lines connected thereto form a chamber sealed as far as the filling nozzle, wherein the filling nozzle forms a free passage to the reaction chamber from outside the cartridge, and a stopper is provided which fits positively and tightly in the filling nozzle in such a way that, when pressed in over a certain distance, fluid is displaced from the filling nozzle towards the reaction chamber.