Block-form cleaners for flush toilets

A block-form cleaner for flush toilets comprising at least two masses of different composition, one of the masses being at least partly surrounded by the other mass or masses, and wherein the surrounded mass and at least one of the surrounding masses contain at least one identical active substance selected from the group consisting of perfume, complexing agent, acid, enzyme, disinfectant, bleaching agent, and mixtures thereof, and the concentration of at least one of these identical active substances in the surrounded mass is at least 1.3 times the concentration of the same active substance In the at least one surrounding mass, wherein each mass contains from 7 to about 85% by weight of surfactant, wherein none of the masses contains a soap in a quantity of greater than 25% by weight, based on the weight of the mass and wherein the masses are constructed so that only or preponderantly the surface of the mass containing the identical active substance in the lower concentrations is initially available for the release of said identical active substance to the surrounding environment.