Abstract: Aldehydes or ketones of not less than 4 or 5 carbon atoms, respectively, are manufactured in a one stage process in the liquid phase by subjecting aldehydes and/or ketones of not less than 2 or 3 carbon atoms, respectively, to an aldol condensation and hydrogenating the resulting olefinically unsaturated aldehyde, the catalyst used for the aldol condensation and hydrogenation containing nickel or cobalt or their mixtures, zinc oxide and at least one of the elements iron, arsenic, antimony, bismuth, gallium, indium, thallium, germanium, tin, lead, cadmium and mercury or compounds of the said elements.