The effect of molecular weight on the yield behaviour and microhardness of melt-crystallized polyethylene has been studied. The influence of the crystallization conditions on the mechanical properties has been examined. It is shown that Tabor’s relationship between microhardness and yield stress applies if the strain rate of the tensile tests is comparable to that employed in the hardness indentation tests. Results are discussed in terms of surface free energy which depends on the number of molecular entanglements segregated on to the surface of the lamellar crystals controlling the yield behaviour of the polymer.