We have reported, for the first time, that macrovoids in asymmetric hollow fiber membranes may be completely eliminated at high elongational draws. The evolution of macrovoids vs. elongational draw Was observed for both single- and dual-layer hollow fiber membranes. The number of macrovoids and the number of macrovoid layer decrease with an increase in elongational draw ratio, while the dimension of macrovoids varies with increasing elongational draw ratio until the macrovoids are fully eliminated. This study indicates that the elongational stress may play a much more important role than our original thoughts on hollow fiber membrane morphology. (C) 2004 Elsevier Ltd. All rights reserved.