At least one alkanolamine is prepared by reacting ammonia with alkylene oxide in a reaction space in the presence of a catalyst to give monoalkanolamine or dialkanolamine or trialkanolamine or a mixture of two or three of these compounds, the distribution of the various alkanolamines within the product spectrum being controlled by means of the temperature in the reaction space, by a process in which the temperature is established by regulating the temperature profile in the reaction space.