Silica nanoparticles with narrow size distribution have been prepared by hydrolysis of tetraethylorthosilicate in ethanol and the presence of ammonia. Variation of reagent concentrations using statistical analyses (factorial design) was used for the first time to optimise the preparation of small sized silica nanoparticles with small standard deviation. Statistical analyses showed there is no significant correlation between reagent concentrations, which have an impact on the resultant particle size. Various agitation methods employed in silica nanoparticle preparation were investigated. Utilisation of an ultrasonic tip has led to dramatic reduction in reaction times, while still providing silica particles of small uniform sizes. (C) 2008 Elsevier B. V. All rights reserved.