A seeding method, using colloidal amorphous silica seed made from geothermal fluid, has been tested as a silica scale prevention method. The effect on silica precipitation of the seed was examined experimentally. The results revealed correlations between the surface area and particle diameter of the seed and the mass of silica precipitated, and indicated that the seed exhibited highly reactive surface properties. The seed was confirmed to be of potential use as a silica removal reagent. Application of the seeding method to geothermal plants will guarantee the self-sufficiency of the latter as regards silica scale removal. (C) 2003 CNR. Published by Elsevier Science Ltd. All rights reserved.