A process for the preparation of urethanes. Urethanes having the general formula R.sub.1 (NHCOOR.sub.2).sub.n are reacted with an alcohol at a temperature of 120.degree. to 400.degree. C. in amounts such that, for every mol of the urethane, at least one mol of the alcohol is present. R.sub.1 is a radical obtained by removing the isocyanate groups from an n-functional organic isocyanate, which isocyanate has a boiling point greater than 100.degree. C. at atmospheric pressure. R.sub.2 is a radical obtained by removing the hydroxyl group from a monohydric alcohol which has a boiling point greater than 140.degree. C. at atmospheric pressure.