An empirical local hardness index is introduced and tested. The usefulness of this new quantity as an intramolecular selectivity descriptor is illustrated for a set of 49 molecules. The proposed local hardness index appears as a good descriptor of the orientation of the electrophilic aromatic substitution, the selectivity of addition reaction as well as the alkylation and acylation of lithium enolates. The sites for the attack by hard species seem to be correctly predicted by the proposed index. (C) 2003 Elsevier B.V. All rights reserved.