1. Patients treated with dense cranial electroacupuncture stimulation (DCEAS) had a significantly greater reduction in the 17-item Hamilton Rating Scale for Depression scores and clinically significant response to treatment than those having sham acupuncture (19.4% vs.8.8%). 2. Neither sham acupuncture nor DCEAS had effects on the platelet serotonin system. 3. In the early phase of selective serotonin reuptake inhibitor treatment for depressed patients, DCEAS could be used as an additional therapy. 4. Neurobiological mechanisms responsible for DCEAS effects warrant further investigation using neuroimaging.