A Study In Patients With Irritable Bowel Syndrome To Measure Hormone Response After Dosing With GW876008 And Gsk561679

Inclusion Criteria: * Has IBS as defined by the Rome II criteria. * Clinical laboratory tests at screening showing no clinically significant abnormalities in the opinion of the Principal Investigator. * Non-tobacco user (abstinence from tobacco use for at least 1 month before the start of the study). Exclusion Criteria: * As a result of any of the medical interview, physical examination, evaluation of mental state and psychiatric history or screening investigations the physician responsible considers the subject unfit for the study. * Subject has any of the following exclusionary psychiatric conditions (Note: current diagnoses are to be based on the M.I.N.I administered at screening). * 1\. A current DSM-IV Axis I disorder such as Dysthymia, Phobia, Major Depression, Obsessive Compulsive Disorder, Body Dysmorphic disorder, or Panic Disorder as a primary diagnosis currently or within 6 months prior to the screening visit. * 2\. A current DSM-IV-TR diagnosis of Antisocial or Borderline Personality Disorder, Dementia, or another current DSM-IV-TR Axis II diagnosis that would suggest non-responsiveness to pharmacotherapy or non-compliance with the protocol; or * 3\. A current (within six months prior to Screening Visit) diagnosis of anorexia nervosa or bulimia; or * 4\. A history of Schizophrenia, Schizoaffective Disorder, or a Bipolar Disorder; or * 5\. Is currently being treated by medication for any of the above psychiatric disorders. Psychiatric medications would include, but not limited to, antidepressants (e.g. SSRIs, SNRIs, TCAs) anxiolytics, antipsychotics * Subjects who, in the investigator's judgement, pose a current, serious or suicidal or homicidal risk or have made a suicide attempt within the past 6 months or have ever been homicidal. * subjects who have taken any medication for the treatment of IBS within 1 month prior to screening except for anti-diarrhoeal medications or laxatives for control of bowel habit which is allowed if at a stable dose for 2 weeks prior to randomisation. * Subjects who are taking NSAIDs including aspirin on a regular basis or within 48 hours of a study day. * Subjects with a history of PUD \<10 years ago. * The subject has a history of, or active eating disorder.