Semi-continuous supercritical antisolvent (SAS) precipitation has been used to produce europium. (EuAc) and gadolinium (GdAc) acetate nano-and micro-particles with the aim of obtaining controlled size and particle size distributions of these superconductor precursors. For both the compounds tailored micro- and nano-particles have been produced from dimethyl sulfoxide (DMSO). Their particle size and particle size distribution were controlled by varying the concentration of the liquid solution injected into the precipitation vessel. Spherical particles with mean diameters ranging from about 0.2 to 10 mum were obtained. The mechanisms that control particle size and particle size distribution were explained in terms of the relative relevance of nucleation and growth processes. (C) 2002 Elsevier Science B.V. All rights reserved.