Investigate Efficacy & Safety of RO4995819 vs. Placebo as Adjunct Tx in Patients w/Major Depressive Disorder

Inclusion Criteria:

Patients are eligible for enrollment in this study if they meet all of the following
criteria:

   1. An outpatient w/a primary diagnosis of major depressive disorder w/out psychotic
   features

   2. Inadequate response to current, ongoing antidepressant tx of SSRI/SNRI.

   3. Having at least 1 but no more than 2 antidepressant treatment failures w/in the index
   depressive episode

   4. Dose/duration of antidepressant treatment in index episode can be verified by
   documentation from one of following:

      1. Med records;

      2. Pharmacy records;

      3. Treating and/or referring physician (indicating medication, dose, dates of
      treatment).

   5. Documentation of clinical/treatment history must be available.

   6. Index depressive episode started w/in 1 year of screening.

   7. Confirmed compliance w/current SSRI/SNRI treatment based on blood screen.

   8. Existing med regimens should be stable for 6 wks prior to screening

   9. 18-65 y.o. at time of consent

10. BMI 18.0 to 35.0 kg/m2 inc.

11. Patients w/reproductive potential must agree to use specified contraceptive protection
   during tx period and for at least 90 days after last dose of study drug:

      - Males w/partners of childbearing potential or partners must use a barrier method
      of contraception or remain sexually abstinent.

      - Females who are not either surgically sterile (tubal ligation, removal of ovaries
      or uterus) or post-menopausal (no spontaneous menstrual periods for at least 1 yr
      confirmed by a hormone panel [FSH and 17βestradiol])must agree to use 2 adequate
      methods of contraception, including at least one method w/ failure rate of < 1%
      per yr (e.g., hormonal implants, combined oral contraceptives, vasectomized
      partner, abstinence).

12. Able to participate and willing to give written informed consent.

Exclusion Criteria:

Patients are excluded from this study if the answer is 'yes' to any of the following:

Current and past treatment history:

   1. Currently receiving tx w/3 or more antidepressants.

   2. Currently receiving tx w/prohibited meds.

   3. Significant ongoing use of high doses of barbiturates, benzodiazepines or other
   anxiolytic drugs.

   4. Previously received RO4995819.

   5. Participated in investigational drug or device study w/in 6 mos of screening or in
   index depressive episode.

   6. History of non-response to Electroconvulsive Therapy (ECT), Vagus Nerve Stimulation
   (VNS),or Repetitive Transcranial Magnetic Stimulation (RTMS).

   7. Planning to begin/change current regimen of individual psychotherapy including
   cognitive behavioral therapy during the 6 week treatment period of the study and the
   first 2 weeks of follow-up.

   8. Present DSM-IV-TR axis I diagnosis except for anxiety comorbidity

   9. Past or present psychotic symptoms.

10. Mood disorder due to medical condition or substance use/abuse/dependence.

11. Established personality disorder

12. Alcohol and/or substance abuse/dependence during the last 6 months.

13. A significant risk for suicidal behavior

14. Past or present neurological disorder.

15. Present eating disorder

16. Abnormal thyroid function.

17. Active upper gastrointestinal tract disease

18. Unstable medical condition that could pose unacceptable risk to the patient in this
   study.

19. Positive result on hepatitis B (HBV), hepatitis C (HCV), or HIV 1 and 2.

20. Positive test for drugs of abuse.

21. Abnormality on 12-lead electrocardiogram (ECG), including a QTcF of ≥450 milliseconds.

22. Lab abnormality

23. Positive pregnancy test, breast feeding,or intention to become pregnant during the
   course of the trial.