The flow of low density polyethylene (LDPE), polystyrene (PS) and a LDPE/PS 33/67 blend of the two through a planar step contraction was visualized. Upstream vortices were generated by the flow of the LDPE but not by the flow of PS. The flow of the LDPE/PS blend generated a convex shaped transparent band which curved around the lip of the step contraction and grew with increasing flow rate. This band is believed to be due to coalescence of the dispersed phase which was observed from SEM photographs of the solidified extrudate. A small upstream vortex was observed during the flow of LDPE at the lowest flow rate. This vortex was located at the midpoint between the corner and the lip of the step contraction. A second vortex was observed at the lip of the die with further increase in flow rate. The two vortices merged at higher flow rates.