fig1 shows a preferred embodiment of the invention in the form of a so called skeletal table 1 which comprises a matrix formulation which does not disintegrate or only slowly disintegrates under the physiological conditions in the stomach it can e g be produced in that granular materials are coated and permeated with permeable acrylic resins and the particles are then compressed without additional fillers in place of acrylic resins it is also possible to use other usually high molecular weight adjuvants which only have a limited solubility in the digestive juices on admixing with the granular material prior to compression an adequate quantity of hollow bodies or foam like structural element particles 2 the specific gravity of the tablet 1 is lowered to such an extent that it floats in the gastric fluid it is also possible to produce a tablet in which a crystalline active substance mixed with microporous structural element powders 2 is compressed it is also possible to provide the active substance particles prior to compression separately with control membranes e g diffusion membranes using per se known processes such as spraying or the like the tablets produced according to the invention cf fig1 can obviously also contain conventional adjuvants such as water insoluble.