Pharmaceutical-clay systems, used as solar radiation shields, obtained by interaction of Na montmorillonite and several pharmaceuticals using two methods of preparation, have been studied. Samples have been prepared by melting the drug onto the clay or by intimate mixing and grinding of both. The shielding ability against solar radiation is improved by use of these preparation methods. Differential thermal analysis and thermogravimetric analysis confirm the steady substitution of water molecules from the interlayer space of the clay by drug molecules, as the amount of the latter is increased. The melting method seems to facilitate access of the drug into the interlayer space of the clay.