A defibrillator (1) comprising electrodes (3), a connection (5) for electrically connecting the electrodes together, a defibrillation circuit (9) connected to the electrodes, and an electrode test system (7), comprising a test initiation device operable to generate a test initiating signal, a test signal generator (15) operable to generate a dc voltage test signal, a test signal switch (17) connected to the electrodes and, on receipt of the test initiating signal, operable to connect the electrodes to the test signal generator for passing the dc voltage test signal to the electrodes, and a test processing device (19) connected to the test signal switch to receive a dc voltage electrode return signal and process the electrode return signal to determine a pass test result or a fail test result for the electrodes.