Following stimulation of the vestibular nerve in the rabbit, respiratory enzyme activities increased in Deiters' nerve cells. The anaerobic glycolysis, measured as 10(-4) microl CO(2) per hour per cell, was found to decrease concomitantly by 25 to 40 per cent, suggesting a Pasteur effect. By contrast, in the surrounding glia the anaerobic glycolysis increased and the respiratory enzyme activity decreased, suggesting a Crabtree effect. The evidence is discussed for a regulatory metabolic mechanism operating between the neuron and its glia. Hypoxia of 8 per cent O(2) caused an increase of both oxygen consumption and CO(2) production in the nerve cells, but did not change the glia values.