In a Total recycle urea-producing system, the improvement is disclosed which consists in providing in the reactor two adjoining but separated reaction spaces, called First and second reaction zones, the surface which separates the two zones being a heat exchanging surface. Fresh ammonia and carbon dioxide are fed with a portion of excess recycled ammonia to the first reaction zone, wherein the reaction is exothermic in character, whereas the condensates from the carbamate decomposition and the remaining portion of the excess recycled ammonia are fed to the second reaction zone, wherein the reactions are of an endothermic nature. By so doing, a better thermal balance in the reactor is obtained, concurrently with improved yields.