The melt rheology of ultrahigh molecular weight polymeric materials characterized by a narrow molecular weight distribution was discussed. The reptation concepts were applied on polypropylenes (PP) and ultrahigh molecular weight polyethylenes (UHMWPE). Metallocene UHMWPE showed a well-developed plateau modulus that approached to 2MPa. It was found that the reptation model predicted the viscoelastic response of the polymers but only in the contour length fluctuation regime. Analysis shows that the molecular weight for the onset of pure reptation for PE took the value of around Mr=800000, much higher than in 1,4-PBd, PIB and PS.