Synaptosomal preparations from rat hippocampus were incubated with methylprednisolone or adrenocorticotropin. High affinity choline uptake was not affected by either hormones. Methylprednisolone however enhanced newly synthesized acetylcholine release in the presence of high potassium or acetylcholine concentrations, while adrenocorticotropin had no effect. Dopamine uptake was inhibited when synaptosomes from septum or striatum were incubated with methylprednisolone. We conclude: a) high glucocorticoid concentrations and not adrenocorticotropin can directly enhance acetylcholine release but only from stimulated cholinergic synaptosomes, and b) high glucocorticoids can reduce dopamine uptake by dopaminergic synaptosomes. The results imply that increased glucocorticoid levels during stress or disease, can directly modulate the neuronal activity of specific cholinergic and dopaminergic systems in the brain.