—This paper makes two contributions towards the logical modelling of inhibition in metabolic networks. First it exposes the logical inconsistency of an existing state-of-the-art metabolic theory. Then it proposes a new model from which the required hypotheses are consistently inferred. Underlying this work is use of nonmonotonic logic programs to represent and reason about competing inhibitory effects on the net concentrations of metabolites in enzyme-catalysed biochemical networks.