A computer model of the metabolism of glutamate, glutamine, γ-aminobutyrate, and the tricarboxylic acid cycle in mouse brain has been constructed in terms of 39 reactions among 19 substances or groups of substances (permitting manipulation of 30 independent variables). The model is divided into two compartments, in conformity with previous models based on indirect evidence, and it is found that this compartmentation is indeed the same as that indicated directly with specifically ¹⁴C-labelled acetate and glucose. The movement of materials between the large and small compartments has been studied; glutamine appears to flow from the small to the large compartment, γ-aminobutyrate in the reverse direction.