Extracts of hypericum perforatum (St. John's wort) have become increasingly popular for the treatment of mood disorders. Hypericum extracts have been approved in Germany for the treatment of mild to moderate depression and are now available in standardized preparations. In the United States, hypericum extracts are frequently purchased as over the counter preparations. Inhibition of the serotonin transporter, similar to clinically used selective serotonin reuptake inhibitors (SSRIs), has been suggested as a possible mechanism of action for the antidepressant properties of hypericum extracts. We propose to study the effects of hypericum extracts on mood states in normal volunteers who are concurrently volunteering under NIMH protocol 98-M-0094 for SPECT imaging of serotonin and dopamine transporter availability with [I-123] Beta-CIT. A placebo-controlled, double-blind, within-subject design will be employed with two two-week periods of drug/placebo administration, clinical assessment and SPECT imaging separated by eleven weeks. We plan to test three hypotheses: 1) that hypericum alters mood state, 2) that hypericum reduces serotonin transporter availability, and 3) that these actions are quantitatively associated with one another.