Irritable bowel syndrome is characterized by abdominal discomfort and bowel habit change. It is increasing worldwide. But the pathophysiology of the irritable bowel syndrome is not proven. So, the treatment's target is the relief of the symptoms.

Small intestinal bacterial overgrowth considered as the cause of the irritable bowel syndrome. Because, it is related to the postprandial abdominal discomfort and the abdominal discomfort could be relieved after taking antibiotics. There are several diagnostic methods for small intestinal bacterial overgrowth. hydrogen breath test is non-invasive method for diagnosis of the small intestinal bacterial overgrowth. But, there is no standardized cut-off value for the hydrogen breath test. So, we want to compare the hydrogen breath test between the irritable bowel syndrome patients and normal people. And then, we want to analyze the efficacy of hydrogen breath test for the diagnosis of irritable bowel syndrome.

Inclusion Criteria:

1. over 19 years old, male and female
2. normal people (control group, who has no abdominal symptoms - diarrhea, constipation etc.)
3. irritable bowel syndrome patients (irritable bowel syndrome means that within the last 3 months abdominal discomfort more than three days for a month and satisfies over the below two items) 1) symptom relived after defecation 2) bowel habit change, the times of defecation changed 3) the change of the morphology of the stool

Exclusion Criteria:

1. patients who do not agree for participation
2. patients who have history for treatment of irritable bowel syndrome
3. patients who is uncontrolled diabetes mellitus
4. patients who have small bowel or large bowel diseases
5. patients who had surgery for abdomen
6. patients who are taking antibiotics, anti-depressants within 1 week
7. patients who are taking proton pump inhibitors or opioids for analgesics
8. patients who have history of bowel adhesion