SUMMARY:The effect of some additives with low molecular weights upon the effective viscosity and slipping in poly(ethylene), poly(propy1ene) and poly(styrene) flow through circular capillaries is studied as a consequence of previous work done. The capillaries are made from different materials: Iron, alloy of copper and zinc, aluminium and poly(tetrafluor0-ethylene). It is noticed that in cases with capillaries made of poly(tetrafluoroethy1ene) the rate of the flow of pure polymers is increased, compared with the rate of the flow through metal capillaries. This effect increases with the increasing of stress and finally reaches 50 percent.One can observe a profound change in slipping and in viscosity behaviour when adding additives with low molecular weight to polymer melts. This effect is characteristic when silicon oil is added to poly(propy1ene) flowing through a poly(tetrafluoroethy1ene) capillary. The relative change of the flow when the conditions are all the same reaches 400%, whereas change through metal capillaries can be neglected.The results show that additives with low molecular weight change the viscosity of the polymer, and when the polymer flows through a poly(tetrafluoroethy1ene) capillary, those additives also change the slipping.