The invention provides a method for the oxidation of carbohydrates with periodate in an aqueous medium, with which method a less than equivalent amount of periodate is used and the periodate is regenerated during the reaction in a separate reaction chamber. The periodate is preferably regenerated electrochemically. The oxidation leads to dialdehyde carbohydrates in which advantageously 30-85% of the available diol groups are oxidized to dialdehyde groups.