We present experimental evidence for the Peltier effect of electrodes that are relevant to the aluminium electrolysis. The electrolyte is therefore always a mixture of molten cryolite and aluminium fluoride saturated with aluminium oxide at 975°C. We find that the aluminium cathode has a large heat production, while the carboncarbon dioxide anode has a small one. The oxygen electrode, on the other hand is cooled down several degrees when the electric current is switched on. The Peltier effect of the oxygen electrode, or the degree of cooling varies with the current, as expected from theory. We propose that irreversible heat effects compensate the reversible (Peltier) cooling of the carboncarbon dioxide electrode in the aluminium electrolysis cell, but that there will be a net cooling effect at electrodes where oxygen production take place.