stability of the nanosuspension is ensured using at least one stabilizer surfactant which will be chosen according to the pharmaceutical active principle and according to the particle size of the nanosuspension piston gap high pressure technology involves using a piston pump to impose a high pressure of the order of 100 to 2000 bar on the dispersion then expanding the dispersion through a homogenizing valve described later on the principle of reducing the size is based firstly on the density of energy generated by the inter particle impacts and by collision between the particles and the valve piston and with the impact ring and secondly on the energy generated by cavitation and by turbulence cavitation is caused by the rapid expansion of the liquid which causes microbubbles of vapor to form devices that employ this technology are marketed for example by the company apv gaulin gmbh the homogenizing valve consists of 3 elements a valve piston 1 a valve seat 2 and an impact ring 3 see fig1 it has been found that the technical problems described hereinabove can be solved if i the valve seat 2 is made partly completely or the exterior surface thereof from the silicon nitride based material described hereinafter and if ii the valve piston 1 is made completely or the exterior surface thereof from said material this silicon nitride based material is strong enough to allow the preparation of the nanosuspension for a long period of time and without the need to dismantle the homogenizing valve in order to change one of the elements.