Blends of PA6/HDPE at different compositions and melt-draw ratio were prepared using a twin-screw extruder with a rectangular slit at 250 degreesC. The morphology results show that at low take up velocity, the final state of deformation is independent of the dispersed phase composition. However, at high take up velocity the drop deformation increases with the composition. To determine a lower limiting concentration, at which coalescence occurs, the average particle volume of the dispersed phase was evaluated. In the concentration range of 1-4 vol% of PA6, the average volume of the particles remains constant (no coalescence) during the stretching process. However, at higher concentrations (>5 vol% of PA6) coalescence takes place and the volume increases with stretching. These results clearly indicate the limiting dispersed phase concentration for coalescence in this system under extensional flow. The approach used here represents a possible technique to separate out the relative contribution of single particle deformation and particle-particle coalescence in dispersed phase fiber formation in an extensional how field. (C) 2001 Elsevier Science Ltd. All rights reserved.