Changes in brain neurotransmitters [5-hydroxytryptamine (5-HT), norepinephrine, histamine and dopamine] were studied in Plasmodium berghei-infected mice and rats. 5-HT and norepinephrine contents of brain decreased significantly in Plasmodium berghei-infected mice and rats, but histamine and dopamine contents remained unaltered. Decreased 5-HT and norepinephrine contents of brain may play a role in cerebral vasodilatation in malaria.