Previous studies demonstrated contents of monoamines in homogenate obtained from salivary glands. Monoamines in homogenate, however, includes that stored in the cells, as well as that released in the interstitial fluids. So far, direct monitoring of autonomic nervous activity within salivary glands has been difficult, and the relationship between neurotransmitter release in the salivary gland and salivary secretion has not been analyzed. Microdialysis was applied to salivary glands and successfully monitored multiple neurotransmitters simultaneously. The present study examined the effects of imipramine, a tricyclic antidepressant, on contents of monoamines in interstitial fluids within submandibular glands of rats. The results revealed the following: (1) that microdialysis allowed detection of norepinephrine and serotonin, but not epinephrine or dopamine; (2) that their concentrations in the dialysate were highly variable and unstable over the first 120 min after probe implantation, but reached a nearly stable level thereafter; and (3) that perfusion with imipramine significantly and dose-dependently increased norepinephrine and serotonin concentrations in the dialysate. These results indicate that the present microdialysis technique offers a powerful tool for detecting changes in sympathetic activity within the salivary glands.