A technique is proposed to relate the weight average molecular weight of linear chains, M-wBL, in low level long chain branched polyethylenes to their linear viscoelastic data. The new method is based on a previously reported empirical technique [Macromolecules 33 (2000) 748 1] and was developed through the use of basic molecular theories. The new technique was applied to model systems whose linear viscoelastic properties were Simulated using the molecular model of Milner et al. [Macromolecules 31 (1998) 9345] and to long chain branched metallocene polyethylenes. It is applicable to branched polyethylenes with low levels of long chain branching. In the case of a branched metallocene polyethylene. the structural parameter, M-wBL, inferred front the theological data together with the GPC data such as M-w or M-n of the sample describes all aspects of the structure of the polymer. In the case of highly branched polymers, a possible modification of the technique is also proposed. (C) 2004 Elsevier Ltd. All rights reserved.