A process for improving the durability, dimensional stability and surface hardness of a wood body is described, in which an untreated wood body is impregnated with an aqueous solution of A) an impregnating agent from the group consisting of 1,3-bis(hydroxymethyl)-4,5-dihydroxyimidazolidin-2-one, 1,3-bis(hydroxymethyl)-4,5-dihydroxyimidazolidin-2-one modified with a C.sub.1-5-alcohol, a polyol or mixtures thereof, 1,3-dimethyl-4,5-dihydroxyimidazolidin-2-one, dimethylolurea, bis(methoxymethyl)urea, tetramethylolacetylenediurea, 1,3-bis(hydroxymethyl)imidazolidin-2-one, methylolmethylurea or mixtures thereof and B) a catalyst from the group consisting of metal or ammonium salts, organic or inorganic acids and mixtures thereof, and wood and impregnating agent are then caused to react while maintaining humid conditions at elevated temperature.