Polyisocyanates are produced by phosgenating a primary polyamine in the presence of at least one compound containing at least one primary and/or secondary alcoholic hydroxyl group in accordance with techniques known in the art. The reactants are used in quantities such that the equivalent ratio of primary amino groups to alcoholic hydroxyl group of from 1:0.005 to 1:0.99 is maintained during the phosgenation reaction. Where phosgenation is carried out in a two-stage process, the compound containing alcoholic hydroxyl groups must at least be present in the required quantity during the second stage. The primary polyamine may optionally be converted into a phosgenatable salt or a carbon dioxide adduct prior to being phosgenated to form the polyisocyanate. The polyisocyanates thus-produced may then be used in the production of polyurethanes or polyamines.