This study is designed to determine whether morning doses of GW679769, taken daily for 1 to 9 days, will promote sleep during the following night without significant post-dose thinking impairment and drowsiness in subjects with primary insomnia.

Inclusion criteria:

• Difficulty going to sleep and/or staying asleep during at least the past 3 months.
• Insomnia must result in significant distress or impairment in functioning at home, socially or at work.
• Otherwise good health with no significant or unstable medical disorder including psychiatric, neurological, endocrine, heart, lung or gastrointestinal disorders, drug/alcohol abuse, cognitive impairment, cancer or chronic pain conditions such as arthritis.

Exclusion criteria:

• History of other sleep disorders such as sleep apnea or restless leg syndrome; regular sleep habits, including bedtime between 9 PM and midnight, nightshift/rotating shift work, frequent napping or planned travel across >2 time zones.
• Use to moderate use of nicotine, caffeine and alcoholic products.