The objective of this study is to determine whether rifalazil can significantly increase peak walking time (PWT) in patients with peripheral arterial disease (PAD).

Inclusion Criteria:

• Male or female patients between 40 and 80 years of age, inclusive.
• The patient has seropositive evidence of Chlamydia pneumoniae defined by immunoglobulin G antibody titers.
• The patient has a diagnosis of intermittent claudication due to PAD at screening.
• The patient's maximal effort PWT is limited only by severe claudication symptoms.
• If the patient is taking cilostazol or pentoxifylline and has been on a stable dose of the medication for at least 6 months prior to screening. Patients who have recently discontinued medications for PAD and/or intermittent claudication must "wash-out" for at least one month prior to screening.
• The patient has been on a stable dose of statin therapy for at least 6 months prior to screening.Patients who have recently discontinued statin therapy must "wash-out" for at least one month prior to screening.
• Male and female patients must agree to use an effective form of birth control throughout the study period.

Exclusion Criteria:

• The patient has critical limb ischemia as evidenced by ischemic rest pain, ulceration, or gangrene.
• The patient has had a major amputation of the leg or any other amputation that limits walking ability.
• The patient is planned for surgical/endovascular intervention for PAD during the course of the study.
• The patient has or is being treated or evaluated for tuberculosis.
• The patient has a known immunodeficient state (e.g., positive for human immunodeficiency virus) or is being treated with immunosuppressive drugs including high dose steroids or cyclosporine.
• The patient has an active infection requiring systemic or oral antibiotics.
• The patient has an uncontrolled, unstable or recently diagnosed autoimmune disease, including but not limited to systemic lupus, inflammatory bowel disease, sarcoidosis, rheumatoid arthritis, or psoriasis. Patients who develop autoimmune disease during the course of the study must be withdrawn.
• The patient's PWT is limited by symptoms other than claudication (shortness of breath, fatigue, angina, or arthritis).
• The patient has a history of alcohol abuse, illicit drug use or drug abuse or significant mental illness.
• The patient has a known or suspected allergy to the study medication(s) or class of study medication (rifamycins) to be administered.
• The patient chronically uses antibacterials or has previously received rifalazil or any rifamycin (e.g. rifampin).
• The patient has uncontrolled hypertension (resting blood pressure > 160/100 mm Hg), uncontrolled moderate to severe congestive heart failure (CHF), or uncontrolled arrhythmic disorders.