Disclosed is a process for converting alcohols to aldehydes and hydrogen peroxide through the use of a methanol oxidase enzyme. The process involves introducing a lower alkyl or lower alkylene alcohol, such as methanol, ethanol, or allyl alcohol, as an aqueous solution into a reaction zone. Methanol oxidase enzyme that is stable in methanol concentrations of at least 0.5% and formaldehyde concentrations of at least 1.0% is also introduced into the reaction zone, which is maintained at an elevated pressure in contact with an oxygen-containing gas. The preferred methanol oxidase enzyme has the properties of the methanol oxidase enzyme produced by Hansenula polymorpha ATCC 34438. Both batchwise and continuous processes are disclosed. Also disclosed is a process in which a catalase is present in the reaction zone to decompose hydrogen peroxide as it is formed, so that the net reaction is the conversion of alcohol to aldehyde. In one aspect of that process, the aldehyde may be removed as a gas and subsequently condensed to an essentially pure liquid.