An aggregometer for measuring and recording platelet aggregation with at least one measurement cuvette having two electrodes, with a device for moving the liquid to be examined and with measurement and evaluation electronics connected to the electrodes via contact elements, is characterized in that the measurement cuvette comprises two adjacently arranged, upwardly open partial spaces which are only connected to one another in the lower region, in that the electrodes are designed as metal spheres inserted in the bottom of the measurement cuvette and in that the device for moving the liquid is a pumping device which can be placed on one of the partial spaces in a substantially sealing manner and which periodically and alternately generates low and excess pressure.