To aid in the understanding of cellulose ultrastructure, computer modelling has been employed to create a model of monoclinic (Iβ) native cellulose. This was achieved by building a chain of cellulose, which was used in a two chain unit cell. An energy minimized microfibril model was created from several of these unit cells. A major advantage of this model is that it is a large scale unconstrained, isolated system. Thus, it facilitates the study of surface as well as central chains and provides a working model of a cellulose microfibril. An extensive analysis was carried out of intermolecular non-bond interactions and how they might contribute to the stability of the structure of crystalline native cellulose. 0969--0239 © 1998 Blackie Academic & Professional