The oxidation of acyloins in aqueous or dry pyridine by mercuric halides yields the corresponding diketones and metallic mercury. With benzoin and anisoin the reactions were of the first order, depending on the concentration of the substrate only, but being enhanced by the presence of water (up to 40% v/v) in the solvent. The reaction was followed by measuring volumetrically the amount of mercury deposited. The mechanism of the oxidation is discussed.