This study will evaluate the effectiveness and safety of the investigational drug talnetant in treating subjects with irritable bowel syndrome (IBS).

Inclusion criteria:

• Subjects will be required to conduct self-assessments of their IBS symptoms using a touch-tone telephone system for the duration of the study (15 weeks).
• Must be diagnosed with IBS consistent with the Rome II criteria.
• Must have normal results from a colonic procedure within 2 years of randomization.
• Must have conducted self-assessments on at least 12 days and have a documented average IBS pain or discomfort score of greater than or equal to 1.5 during the two-week screening phase.

Exclusion criteria:

• Self-assessment of no stool for 7 days during the two-week screening phase.
• Clinically significant abnormal laboratory tests.
• Current evidence or history of various conditions, comorbidities, or surgeries such as Irritable Bowel Disease (IBD), gastrointestinal surgeries, and diverticulitis.
• Inability to use the touch-tone telephone system.
• Hypersensitivity to quinolone antibiotics or quinolone derivatives.
• Diagnosis of a psychiatric disorder within the past 2 years and not on a stable dose of medication for at least 6 months.
• Women who are pregnant, breast feeding, or planning to become pregnant during the study.

Permitted medications: The subject is allowed to take any of the following medications, provided they maintain a stable dose for at least 30 days prior to the Screening visit and throughout the remainder of the study:

• Antidepressants, except REMERON
• Antihypercholesterolemics
• Iron supplements
• Bulking agents
• Fiber supplement
• Thyroid replacement therapy (levothyroxine)
• Antipsychotics
• Cox-2 inhibitors (CELEBREX)

Prohibited medications: Subjects must stop taking any medications they are taking to treat their IBS symptoms and must not have taken any of the prohibited medications at least 7 days prior to the Screening visit and must remain off these medications for the duration of the study.

• Anticholinergics (dicyclomine, hyoscyamine, propantheline)
• Cholinomimetic (bethanechol, pyridostigmine, tacrine, physostigmine)
• All narcotics (morphine, codeine, TYLENOL #3, propoxyphene, either alone or in combination)
• Tramadol hydrochloride (ULTRAM)
• Colchicine
• Orlistat (XENICAL)
• Misoprostol, alone or in combination (ARTHROTEC, CYTOTEC)
• 5-HT3 receptor antagonists (ondansetron, tropisetron, dolasetron, granisetron, mirtazapine, cilansetron, alosetron)
• Tegaserod (ZELNORM)
• Gabapentin
• Lupron
• Antacids containing magnesium or aluminium
• Antidiarrheal agents
• Bismuth compounds
• Prokinetic agents (cisapride, metoclopramide)
• Sulfasalazine
• Laxatives
• Cholestyramine