Bare and PEGylated silica spheres have been synthesized and characterized in order to study their potential application as intravenous drug-delivery vectors. Solubility under physiological conditions (in simulated body fluid) as well as standard protein adsorption experiments (immobilization of bovine serum albumin, BSA) were carried out in order to analyze the stability and the potential avoidance of the reticuloendothelial system (RES) achieved after PEGylation. The influences of the chain length of the PEG, as well as, of the temperature in the esterification reaction were also analyzed. (C) 2007 Elsevier B.V. All rights reserved.