Work on the interdependence of neurons and glia has focused not only on CO2 fixation in astroglial cells but also in 13C-glucose metabolism in these cells. Astroglia, in culture, have been found to release products of C02 fixation into the surrounding medium with only a relatively small fraction of the products remaining in the cells. In mixed cultures of astroglial and neurons, however, approximately 90% of the labelled products were found within the cells suggesting that when these cells are in intimate contact there is a transfer of products from one cell to anther rather than a release of products into the extracellular medium. The anapleoric C02 fixation reaction occurring in glial cells may therefore serve to replenish essential metabolites in both neurons and astroglial cells.