The purpose of this study is to evaluate the safety and efficacy of different doses of asimadoline in the treatment of patients with irritable bowel syndrome.

A randomized, dose-ranging, double-blind, placebo-controlled study designed to evaluate the efficacy and tolerability of three dose levels of asimadoline in subjects with IBS.

Inclusion Criteria:

• Males and females aged 18-79
• Must sign an ICF
• Females of childbearing potential must have a negative pregnancy test at screening and must adhere to contraception throughout the trial
• Must have been diagnosed with IBS as a result of having at least 6 months, not necessarily consecutive, in the preceding 12 months of recurrent symptoms of abdominal discomfort or pain associated with at least 2 of the following: 1)relieved with defecation; 2)onset associated with a change in stool frequency; 3)onset associated with a change in stool form
• Must demonstrate a willingness to comply with daily telephone diary entry

Exclusion Criteria:

• Any subject with evidence of a biochemical or structural abnormality of the digestive tract or other co-morbid illness that might impact the ability to interpret the safety and efficacy data
• Pregnant or breastfeeding females
• Refusal to discontinue prohibited concomitant medications
• Use of an investigational drug or participation in an investigational study within 30 days of screening
• Inability or unwillingness to use the touch-tone telephone data entry system