This treatment pilot study will investigate clinical efficacy and adverse effects of magnetic seizure therapy (MST) in patients currently experiencing a unipolar or bipolar depressive episode. The investigators will perform add-on tests to assess clinical and cognitive response to treatment. It is hypothesized that MST will have an antidepressant efficacy with a beneficial neurocognitive adverse effect profile.

Inclusion Criteria:

• Patient is diagnosed with a severe major depressive episode
• Patient is in a chronic current MDE and/or has had a history of recurrent MDEs
• Patient has not had an acceptable clinical response due to failure with at least 2 antidepressant treatments during the current episode
• Patient has a score > 20 on the HAMD24
• Patient is stable on current psychotropic medication for at least 4 weeks
• Patient is > 25 and < 80 years

Exclusion Criteria:

• Atypical Depression or psychotic depression (according to DSM IV)
• Other relevant psychiatric axis I or axis II diseases
• Relevant neurological diseases
• Relevant cardiac or pulmonary diseases with enhances anesthesiological risk (ASA Score > 3)
• Patient is currently enrolled in another investigational study not associated with the current study
• Patient has a history of, or evidence of, significant brain malformation or significant head injury