We have studied the deprotonation of sulfuric acid in small water clusters containing up to nine water molecules. Our main interest was to find out if the sulfuric acid can be completely deprotonated in such small clusters. Our results show that the fully deprotonated clusters are energetically very close to the partially deprotonated clusters. Thus, in clusters containing eight or more waters the sulfuric acid can be completely deprotonated. (C) 2004 Elsevier B.V. All rights reserved.