The invention relates to a method for generating an atmosphere intended for the heat treatment of metal parts in a furnace, according to which a mixture comprising gaseous CO and methanol in the form of fine droplets or vapour is introduced into at least one phase of the treatment cycle or at least one area of the heat treatment furnace, in such a way as to produce a reaction between the CO and the methanol in the furnace to form a mixture of hydrogen and CO according to the reaction: CH3OH + CO -> 2CO + 2 H2, the CO having been obtained upstream of said introduction by means of a reaction between a hydrocarbon or a mixture of hydrocarbons and CO2 in a CO generator.