Caffeine (100 and 200 mg/kg, 30 min., i.p.) selectively altered the regional utilization of monoamines in the brains of mice. This depended upon the specific neurotransmitter and metabolite studied. Caffeine increased serotonin (5HT) utilization a dramatic ten-fold in the OB but decreased 5HT utilization in the HT. No 5HT changes were seen in other brain regions. Caffeine markedly increased norepinephrine (NE) utilization in the olfactory bulbs (OB), olfactory tubercles (OT), prefrontal cortex (PC), amygdala (AMY), hypothalamus (HT) and hippocampus (HC). Caffeine increased dopamine (DA) utilization in the OB, OT, PC, septum (SP), HT and thalamus (TH) but by various metabolic routes. The selective regional alterations in monoamine utilization produced by caffeine may be relevant to caffeine's central stimulatory effects. Limbic structures are predominantly involved. These changes may have important clinical and research implications. For example, the profound effect of caffeine on OB monoamines indicates that it may serve as a meaningful tool in olfactory research, including the bulbectomy model. Caffeine may also be useful in other limbic system behavioral models.