A model is proposed for the mechanism of action of the glucose transport system of the human erythrocyte. The model is based on the possibility of there being interaction through the membrane between superficially disposed protein subunits, these units being embedded within the bimolecular lipid layer, anchored to the aqueous phase, perhaps mobile in the plane of each face of the membrane. The subunits have the ability to bind sugar and, when associated with the symmetrical protein at the opposite face of the membrane, transfer sugar across the membrane. Evidence for the model is presented. The possibility that this model may also be a model for the cell membrane as such is briefly touched upon.