The phosphodiesterase inhibitor and putative antidepressant rolipram (0.3-30 mg/kg i.p.) stimulated the accumulation of dopa following inhibition of the aromatic amino acid decarboxylase with 3-hydroxybenzylhydrazine HCl dose-dependently in all brain regions investigated, suggesting that both dopamine and noradrenaline synthesis was enhanced. The stimulatory effect of rolipram on dopa accumulation in dopamine rich regions persisted even after pretreatment with gamma-butyrolactone which by itself increased dopa accumulation three fold. Following inhibition of catecholamine synthesis with alpha-amethyl-p-tyrosine rolipram accelerated the disappearance of noradrenaline and slowed the disappearance of dopamine. At low doses rolipram tended to reduce the pargyline-induced accumulation of 3-methoxytyramine. Rolipram attenuated the accumulation of 5-hydroxytryptophan in the neocortex and the diencephalon of 3-hydroxybenzylhydrazine HCl pretreated rats. The data suggest that rolipram enhances noradrenergic transmission by direct stimulation of tyrosine hydroxylase and by an increase of neuronal activity. Despite a stimulatory effect on tyrosine hydroxylase rolipram does not appear to alter dopamine release and metabolism to a large extent. In view of the occurrence of head-twitches the rolipram-induced reduction of 5-hydroxytryptamine metabolism may be due to feedback inhibition.