Northern blot analysis was used to examine the effects of glucocorticoids on neurotrophin mRNA expression in the rat cerebral cortex and hippocampus. The results show that 3 days after adrenalectomy the mRNA levels for nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) decreased significantly in both these regions. In adrenalectomized animals given dexamethasone replacement the mRNA levels for the three neurotrophins were restored to control levels. The effect of a single dose of dexamethasone (5 mg/kg) administered i p. to intact animals on the expression of neurotrophins was also examined. NGF and NT-3 mRNAs showed a 2.5-fold and a 1.4-fold increase, respectively, during the first 4 h after the injection. The increase was followed by a decrease, with levels -50% of control 24 and 48 h after the injection. In contrast, the level of BDNF mRNA did not change during the first 10 h after the injection, but decreased to 70% of control 48 h after the injection. These data indicate that glucocorticoids regulate neurotrophin mRNA expression both in the cortex and in the hippocampus, and suggest further that the known effects of glucocorticoids on neuronal survival in the brain could be due to changes in the levels of neurotrophins in the brain.