Diadochokinesia or diadochokinesis is the ability to make antagonistic movements in quick succession, alternately bringing a limb into opposite positions, as of flexion and extension or of pronation and supination. Speech-language pathology defines it as the speed necessary to stop a determined motor impulse and substitute it with its opposite. The relative timing of this kind of movements is also called alternate motion rates (AMR) or sequential motor rates (SMR).

Loss of this ability, called dysdiadochokinesia, is a characteristic sign of cerebellar diseases. Many clinical tests may be employed to test for such disturbances.