The intracerebral injection technique was used to apply dopamine directly into dopamine-containing areas of the mesolimbic system, the nucleus accumbens septi, tuberculum olfactorium and nucleus amygdaloideus centralis. 200 mug dopamine injected bilaterally into the nucleus accumbens septi caused a stereotyped sniffing behaviour and hyperactivity but only a periodic hyperactivity developed after similar injections into the tuberculum olfactorium and no change in behaviour was observed following injections into the nucleus amygdaloideus centralis. After pretreatment with nialamide, the effects of intracerebral dopamine were enhanced, doses of 1-50 mug dopamine causing consistent stereotyped sniffing and a dose-dependent hyperactivity on injection into the nucleus accumbens septi or tuberculum olfactorium. The effects initiated from the nucleus accumbens septi were most marked. In addition, 50-100 mug dopamine injected into the tuberculum olfactorium caused a periodic biting behaviour. Biting was not observed after injections into the nucleus accumbens septi and, even in the presence of nialamide, injections of dopamine into the nucleus amygdaloideus centralis failed to cause any change in motor behaviour.