Basal tryptophan hydroxylase activity was measured in several serotonergic nerve terminal regions of the rat brain and was found to vary from one terminal region to another. Acute administration of methamphetamine produced a marked decrease in tryptophan hydroxylase activity in all serotonergic nerve terminal regions of rat brain examined. This decrease was antagonized in a regionally selective manner by propranolol. In contrast, haloperidol did not produce a similar antagonism. The results are discussed in the context of the previously reported efficacy of large doses of propranolol in some schizophrenic patients.