This is a multi center, double blind placebo controlled, two-way crossover study in patients with Insomnia suffering from difficulty in falling asleep and staying asleep. This study intends to assess the efficacy of Zaleplon AP in improving sleep parameters, comparing to placebo.

Inclusion Criteria:

• Subjects between the ages of 18 and 65 years of age
• Subjects that meet DSM IV diagnostic criteria for Primary Insomnia
• Subjects that report a time in bed ≥6.5 and ≤9 hours
• Subjects that report on a one week sleep diary (on at least 3 of 7 nights) TST ≤6.5 hours
• Subjects that report on a one week sleep diary (on at least 3 of 7 nights)Wake time after sleep >1.0 hour
• Subjects that report on a one week sleep diary (on at least 3 of 7 nights) ≥30 minutes time to sleep onset
• On two nights of PSG screening a mean WASO of ≥60 minutes with neither night less than 45 minutes
• On two nights of PSG screening a mean LPS of ≥20 minutes with neither night less than 15 minutes
• On two nights of PSG screening a TST of ≤6.5 hours on each of the two nights
• Body mass index of 18 - 34 inclusive
• Subjects that report a median habitual bedtime between 9:00pm (21:00 hours) and 12:00am (00:00) on a one week sleep diary (based on 3 or more nights).

Exclusion Criteria:

• Participation in another drug clinical trial within 1 month prior to first screening diary day (calculated from the previous study's last dosing date).
• On screening PSG night 1 an AHI >10 (apnea hypopnea index)
• On screening PSG night 1 a PLMAI ≥10 (periodic limb movements with arousal)
• Subject has a circadian rhythm disorder including shift work or the need to travel ≥3 time zones during the course of the study
• Subject has any other sleep disorder (e.g. Restless Legs Syndrome )
• Use of any drug known to effect sleep or wake functions within 5 half lives of the drug or two weeks, whichever comes first.
• Subject with a history (past year) of alcohol or substance abuse
• Subject that needs to smoke during the sleep period time
• Subject that reports habitual napping (more than 3 times per week)
• Subject has currently or a significant history of seizures, sleep apnea or restless leg syndrome or other sleep disorders which, in the opinion of the investigator responsible, contraindicates his/her participation
• Subjects with a recent history of clinically defined GERD, peptic ulcer or any gastrointestinal surgery other than appendectomy or herniotomy which, in the opinion of the investigator responsible, contraindicates his/her participation
• Subject with any gastrointestinal disorder likely to influence drug absorption, or with any history of inflammatory bowel disease, intestinal obstruction, irritable bowel syndrome, severe gastrointestinal narrowing, or frequent nausea or emesis, regardless of etiology which, in the opinion of the investigator responsible, contraindicates his/her participation
• Subjects suffering from any Axis 1 Psychiatric Disorder that in the opinion of the investigator responsible may interfere with full participation
• Subject has significant history of cardiac, pulmonary, hepatic or renal disease or other condition or any major complication/illness which, in the opinion of the investigator responsible, contraindicates his/her participation.
• The subject has any clinically important abnormal finding as determined by a medical history, physical examination, electrocardiogram, or clinical laboratory tests, as determined by the investigator
• Subject is taking CNS-active drugs (including herbal products with CNS effects), known to affect the sleep/wake cycle including but not limited to anxiolytic, hypnotics, antidepressants, sedating H1 antihistamines, systemic steroids, anticonvulsants, narcotic analgesics, respiratory stimulants respiratory decongestants, OTC and prescription diet aids, OTC and prescription stimulants, St. John's Wort, and melatonin.
• Females who are pregnant or nursing.