The polarographic behaviour of the acetyl- and benzoyl pyridine N-oxides shows the same type of anomalies as those which have previously been mentioned in the case of the corresponding formyl pyridine N-oxides: when the substituent lies in the 2 or 4 position, the N-oxide group and the carbonyl group are simultaneously reduced, the 3-isomers being normally reduced at all pH values. From the ultraviolet spectra, one concludes that the carbonyl group is hydrated, but not so strongly as in the case of the formyl pyridine N-oxides.