AbstractIn a preceding communication it has been shown, that the energy involved in the process of stretching to rupture of air dry isotropic cellulose filaments is large enough to bring about a considerable drop in the average molecular weight of the material if this energy should, to any appreciable extent, be connected with the rupture of primary valencies in the molecular chains.Viscosity determinations in two different solvents show however, that there is no detectable difference in viscosity between solutions of unstretched and stretched filaments. Consequently, no molecular chains are broken in the process of deformation and rupture of cellulose filaments.