The trophic model for the River Thames, England, developed by the International Biological Programme (IBP) is probably the most complete ever constructed for a riverine ecosystem. A Mark 2 model is presented here, constructed using ECOPATH II. The model reinforces many of the conclusions of the earlier study and exposes certain weaknesses. In particular, the trophic role of the main fish populations and detritus is revised. Certain improvements that could be made to the Mark 2 model are identified, relating to the inclusion of incoming solar energy and to the efficiency of the community in converting solar energy to animal and plant tissue.