Liquid organic polyisocyanates containing carboxyl and/or carboxylate groups are prepared by reacting liquid multicomponent mixtures of aromatic polyisocyanates having an isocyanato content of about 10 to about 20% by weight and a viscosity of about 8 cP to about 10,000 cP at 25.degree.C withA. a compound which contains carboxylate groups and hydrogen atoms which are reactive with isocyanate groups; orB. a hydroxycarboxylic or mercaptocarboxylic acid, wherebyBa. at least partial conversion of the carboxyl group into the corresponding carboxylate group by neutralization with a base is carried out simultaneously with or after the isocyanate addition reaction orBb. the hydroxycarboxylic acid or mercaptocarboxylic acid is of the kind in which the carboxyl groups are much less reactive with the isocyanate groups than are the hydroxyl or mercapto groups, the quantitative proportion of the reactants being so chosen that the products of the process have an isocyanate content of 10 to 40% by weight and a carboxyl or carboxylate group content of 0.1 to 10% by weight. The polyisocyanates can be used to make inorganic-organic plastics.