Comparison with the Wiener number and the molecular connectivity index, a novel set of Wiener indexes (W-m(p), W-m(pc), W-m(c) and W-m(ch)) were defined, which are named the extended Wiener index. The potential usefulness of the extended Wiener index in QSAR/QSPR is evaluated by its correlation with a number Of C-3-C-8 alkanes and by a favorable comparison with models based on molecular connectivity index. (C) 2002 Elsevier Science B.V. All rights reserved.