The method specified consists in heating a test portion in an acid medium to depolymerize any to paraldehyde present and to entrain, by distillation, both regenerated acetaldehyde and the monomeric acetaldehyde originally present. Reaction of the acetaldehyde in the distillate with an excess of sodium hydrogen sulphite solution. Iodometric titration of the residual sodium hydrogen sulphite solution. The method is applicable to products having total acetaldehyde contents equal to or greater than 0,004 % (m/m). It has also been approved by the International Union of Pure and Applied Chemistry (IUPAC). ISO 753/1 to iso 753/11 cancel and replace ISO Recommendation R 753-1968.