The saliva level of free 3-methoxy-4-hydroxyphenylglycol (MHPG) in 16 outpatients with anxiety disorders was determined by gas chromatography-mass spectrometry. The anxiety level of the patients was scored by the Hamilton Anxiety Scale (HAS) before and after a one-week drug treatment with alprazolam. The saliva level of free-MHPG at the subjects' first visit to the hospital was significantly higher than that of the control subjects and was reduced by the one-week alprazolam treatment. The post-treatment level of MHPG in patients who showed good response to the treatment was significantly less than the pretreatment level, but there was no significant difference between pre- and post-treatment levels of MHPG in poor responders. There was no correlation between the MHPG level and the HAS score at the first hospital visit. The MHPG levels after the treatment correlated with the HAS scores. The reduction of the anxiety level as scored by the HAS correlated with the reduction of the MHPG level. These results indicate that the free saliva MHPG level may be a useful indicator for assessing not only the level of anxiety but also the response to drug treatment for anxiety in these patients.