Measurements of the complex shear compliance(J* = J′ − iJ″)have been carried out for three polyethylene samples of increasing weight average to number average molecular weight ratios (M̄w/M̄n) of 19, 70, and 110. The measurements extended to temperatures well above the crystalline melting points of the polyethylenes and over a frequency range from 25 to 2500 cps. A sudden increase in compliance occurred at all frequencies at the melting points of each type of polyethylene; there were no marked differences in dynamic mechanical behavior below the melting points. Above the melting points values of storage compliance (J′) were very nearly the same for all the polyethylenes but differences in the loss compliance (J″) were found. In particular at higher frequencies (1300 cps) values ofJ″ diverged with temperature in ascending order asM̄w/Mnincreased. Values of mechanical loss tangent (J″/J′) showed sudden jumps at the melting points but them was no evidence of maxima or peaks at these temperatures. Attempts to superpose the data in the melt were unsuccessful as values ofJ″ at various temperatures could not be shifted into coincidence even though values ofJ′ superposed fairly well. The superposition anomalies are tentatively ascribed to the presence of a secondary maximum in the loss compliance vs frequency characteristics of the materials while the secondary maximum, in turn, is attributed to either (1) a split molecular weight distribution with two separate maxima, or (2) a β mechanism involving the motion of very long branches.