The effect of the anti-muscarinic and psychotomimetic agent, scopolamine, on the accumulation of 14C-catecholamines formed from 14C-tyrosine administered intra-cerebrally to the mouse was studied. In doses from 3 to 30 mg/kg, scopolamine was found to decrease the cerebral accumulation of 14C-dopamine and 14C-norepinephrine but increase the accumulation of 14C-normetanephrine. Similar effects on 14C-catecholamine accumulation were observed when 14C-DOPA was used as substrate. These effects are causally postulated to be related to blockade of inhibitory muscarinic responses which decrease CA output. The relevance of these findings to the toxic psychosis induced by scopolamine is discussed.