AbstractA theory of the excluded volume of branched molecules has been developed. The model of the branched molecule is a main or backbone string of beads from which side branches (which are themselves unbranched) originate. Each of these beads has the property of the Kuhn statistical chain element. The calculation is based on the Fokker‐Planck equation as used by Hermans and collaborators. The differential equation obtained therefrom is not solved, but the average squared distance between two segments on the main chain is obtained. It is found that this quantity\documentclass{article}\pagestyle{empty}\begin{document}$_{Av} $\end{document}contains a term proportional to (t−p)3/2power, which term arises from the contribution of the branches. The radius of the molecule, which can be measured by light scattering techniques, contains a term proportional to the molecular weight to the three halves power if the length of the branches does not depend on molecular weight. It is suggested that the dependence on molecular weight of the relation between molecular size and branching could be used as an experimental check of the the