Abstract: The present invention relates to heat-curable, cyclic isocyanate addition productsi) which are the reaction products of a polyisocyanate having two or more isocyanate groups with a compound containing two or more isocyanate-reactive groups andii) in which at least 10% by weight of the reaction products are in the form of cyclic groups containing urea and/or urethane groups.The present invention also relates to a process for the preparation of these cyclic isocyanate addition products and to the products obtained by curing these compositions at elevated temperatures, e.g., coatings, adhesives, molded articles, elastomers and foams.