Extrusion/spheronisation for the production of pharmaceuticals pellets, includes four unit operations, and the first: wetting, requires the determination of optimal mass proportions between solid (powder) and liquid. This study proposes a method to determinate these proportions for a controlled feasibility. The wetting curves obtained in trials for three wet granular media are located on a hydro-textural diagram. The determination of additional hydric limits provides an empirical relation making it possible to locate a wetting optimum. (C) 2008 Elsevier B.V. All rights reserved.