Phase segregation in melt-extruded blends of polyethylenes that differ considerably in molecular weight was found to exert diverse degrees of influence on various measured mechanical properties. The instantaneous tensile deformation properties were insensitive to phase segregation while the high-strain tensile deformation behavior was found to be strongly influenced by phase segregation. We also found that certain degrees of phase segregation can favor the plane stress fracture resistance of the blend. Finally, we will also report on the influence exerted by the difference in molecular weight between the blend components on the phase segregation and consequent mechanical performance of the blends.