Glucose metabolism in crucian carp exposed to 3 days of hypoxia was studied using 14C-2-deoxyglucose (14C-DG) as a tracer. Four brain areas were investigated by autoradiography; telencephalon, optic tectum, cerebellum and the vagal lobes. In addition seven tissues were investigated by scintillation counting. No significant effects of hypoxia were observed in the brain areas studied with autoradiography. Scintillation counting revealed that hypoxia increased the uptake of 14C-DG in the brain as a whole, as well as in the heart and red muscle, while no changes were observed in gills, liver, intestine and white muscle. The results indicate a higher glucose demand in brain, heart and red muscle under hypoxic conditions, suggesting that these tissues maintain a relatively high activity in hypoxia and have to increase their glycolytic activity to compensate for reduced oxidative ATP production. Other tissues may primarily rely on metabolic depression to compensate for the hypoxia-induced fall in oxidative phosphorylation.