Abstract: Hydroxylammonium salts are manufactured by a process comprising the catalytic reduction of nitric oxide with hydrogen in a dilute aqueous mineral acid in the presence of a suspended platinum catalyst at an elevated temperature, wherein the reaction is carried out in vessels of which the walls consist of conventional copper-containing austenitic chromium-nickel steels which contain from 16 to 28% by weight of chromium, from 32 to 50% by weight of nickel, from 1 to 4% by weight of molybdenum, up to 4% by weight of copper and at most 0.1% by weight of carbon and which in addition contain an amount of titanium which is at least 5 times the amount of carbon but is not more than 1% by weight, or an amount of niobium or tantalum which is at least 8 times the amount of carbon but is not more than 1.5% by weight.