This study is designed to investigate whether GC1008, an antibody that neutralizes TGFb, is safe in treating patients with idiopathic pulmonary fibrosis. The highest dose without excessive side effects will be identified. Tests will determine how long GC1008 is in the body and how it is excreted.

Inclusion Criteria:

• Willing and able to provide written informed consent prior to any study-related procedures.
• Patients should have an established diagnosis of IPF.
• Pulmonary Function Tests (PFTs): FVC ≥ 50% and DLCO ≥ 25% of normal predicted values.
• Able to walk at least 500 feet (150 meters) during the 6-minute Walk Test (6MWT). During the 6MWT the patient must not require greater than 51/min supplemental oxygen to maintain oxygen saturation > 80%

Exclusion Criteria:

• Women who are pregnant or lactating; or who plan to become pregnant within 9 months after the infusion.
• Women of childbearing potential or men who are considering fathering a child unless taking medically acceptable contraceptive precautions;
• History of clinically significant environmental exposure, including dust, molds, asbestos, pigeons or other birds that may result in interstitial lung disease, or ingestion of a drug known to cause pulmonary fibrosis such as bleomycin.
• History of clinically significant respiratory diseases other than IPF.
• History of clinically significant cardiac, hepatic, or renal disease.
• History of cancer, precancerous state (e.g. familial polyposis, BRCA1, BRCA2), other than non-melanomatous skin cancer, within 5 years prior to Screening.
• Use of any investigational drug administered as part of a clinical trial within 12 weeks before Screening.
• Other pathology that might interfere with the assessment of the safety or efficacy of the test article.
• Other clinically significant, uncontrolled medical condition that, in the Investigator's opinion, might interfere with the assessment or follow-up.