In this study, patients with major depressive disorder (MDD) who have insomnia symptom are treated with Seroquel XR in an open-label manner for a 4-week period with repeated measurements of insomnia symptoms and sleep parameters using polysomnography.

Patient Inclusion Criteria:

• Men and women aged between 20 and 65
• Diagnosis of major depressive disorder as assessed by Structured Clinical Interview for DSM-IV (SCID-IV)
• A score of 1 or greater on any of the sleep items (items 4, 5, 6) from the Hamilton Depression Rating Scale (HDRS)
• Provision of written informed consent

Healthy Control Subject Inclusion Criteria:

• Healthy Men and Women aged between 20 and 65
• Provision of written informed consent

Exclusion Criteria:

• Presence of any major physical or neurological illness (e.g.，head trauma， epilepsy，seizure，stroke，cerebral tumor，multiple sclerosis，cerebrovascular disease, narrow-angle glaucoma, drug hypersensitivity，etc.)
• Diagnosis of any Axis I disorder other than major depressive disorder or presence of symptoms requiring hospitalization
• Drug abuse in past 3 months
• Women who are pregnant，breastfeeding, or planning pregnancy
• Contraindications to drugs used in the study (e.g., allergy, intolerance, etc.)
• Unstable medical illness or severe abnormality in laboratory test at screening assessment
• Increase in blood glucose, lipid, and calcium levels at screening
• Low blood pressure at screening assessment
• Intelligence quotient below 80
• Use of any of the following cytochrome P450 3A4 inhibitors in the 14 days preceding enrolment including but not limited to: ketoconazole, itraconazole, fluconazole, erythromycin, clarithromycin, troleandomycin, indinavir, nelfinavir, ritonavir, fluvoxamine and saquinavir
• Use of any of the following cytochrome P450 3A4 inducers in the 14 days preceding enrolment including but not limited to: phenytoin, carbamazepine, barbiturates, rifampin, St. John's Wort, and glucocorticoids
• Administration of a depot antipsychotic injection within one dosing interval (for the depot) before randomisation
• Substance or alcohol dependence at enrolment (except dependence in full remission, and except for caffeine or nicotine dependence), as defined by DSM-IV criteria
• Opiates, amphetamine, barbiturate, cocaine, cannabis, or hallucinogen abuse by DSM-IV criteria within 3 months prior to enrolment
• Previous enrolment or randomisation of treatment in the present study.
• Participation in another drug trial within 4 weeks prior enrolment into this study or longer in accordance with local requirements
• Medical conditions that would affect absorption, distribution, metabolism, or excretion of study treatment
• A patient with Diabetes Mellitus
• An absolute neutrophil count (ANC) of <= 1.5 x 10^9 per liter
• Insomnia from other causes of medical or neurological diseases
• Involvement in the planning and conduct of the study