In brain areas enriched of dopaminergic nerve terminals presynaptic dopamine (DA) autoreceptors control the state of activation of tyrosine hydroxylase (TH) by regulating the extent of phosphorylation of the enzyme. Evidence is presented indicating that this autoinhibitory control may involve a decrease in the cyclic AMP-dependent activation of TH through an inhibitory coupling of presynaptic DA autoreceptors to adenylate cyclase. As indicated by the insensitivity of the DA inhibition of TH to changes in the extracellular concentrations of Ca++, to the addition of the Ca++ ionophore A 23187 and of different K+ channel blockers, a reduction of Ca++ influx and an increase in the K+ channel activity do not seem to be involved in the presynaptic regulation of TH activity by DA autoreceptors at least under basal conditions.