Six polyethylenes which differed widely in the degree of crystallinity were studied. The crystallinity was determined from density measurements. Both the density and the dynamic mechanical measurements were made over the temperature range from 25°C to above the melting point of the material.The dynamic shear modulus drops rapidly as the melting point is approached. The mechanical damping goes through a maximum near 60°C and then through a minimum just below the melting point. It is possible to predict the density of any of the polyethylenes at any temperature below the melting point from the value of the shear modulus at the same temperature. The more crystalline materials have the higher shear moduli and the higher melting points.