Two animal models were used to investigate the effect of lowered central noradrenaline levels on two dopamine-dependent behavioural parameters in the rat. Newborn rats were injected with 6-hydroxydopamine or adult animals had bilateral electro-lesions placed in the region of the locus coeruleus in the brain stem. The effect of these two lesions on amphetamine- and apomorphine-induced stereotyped behaviour and on haloperidol-induced catalepsy was studied. 1. Both 6-hydroxydopamine treatment at birth and bilateral locus coeruleus lesions specifically harmed the ascending dorsal noradrenergic pathway, causing significant decreases in cortical and limbic forebrain noradrenaline concentrations. 2. Both types of lesion had no apparent effect on stereotyped behaviour induced by either amphetamine and apomorphine. 3. Both types of lesions significantly enhanced the cataleptic response induced by varying doses of the neuroleptic agent haloperidol. 4. The results indicate that noradrenergic function may partly influence some dopaminergic mechanisms, and its possible site of action in terms of neostriatal and limbic populations of dopamine receptors is discussed.