To evaluate the safety and tolerability of FG-3019 in subjects with Idiopathic Pulmonary Fibrosis (IPF) and the efficacy of FG-3019 for attenuating fibrosis in these subjects.

Major Changes: FGCL-3019-049 Protocol Amendment 3 offers long-term extension of treatment with FG-3019 to eligible Cohort 1-EX (approximately 14 subjects) and Cohort 2 (approximately 28 subjects) subjects who complete the Week 48-EX and Week 48 assessments described in Protocol Amendment 2, respectively. A subject is eligible for long-term extension of treatment if the investigator, after discussion with the Fibrogen Medical Monitor, believes that the subject would benefit from continued treatment with FG-3019.

Main Inclusion Criteria:

1. Age 35 to 80 years, inclusive.
2. Clinical diagnosis of IPF by high resolution computed tomography (HRCT) scan (and in some cases by surgical lung biopsy) and reduced lung function (forced vital capacity).
3. History of IPF of 5 years duration or less.
4. Evidence of progression of IPF within the last 3-12 months for Cohort 1, or within the last 18 months for Cohort 2 before screening.
5. Women of childbearing potential, and men, must be willing to use a medically acceptable method of contraception during the trial and 3 months after the last dose of study drug.

Main Exclusion Criteria:

1. Women who are pregnant or nursing.
2. History of any other types of lung or heart disease and any other medical conditions that, in the opinion of the investigator, would preclude the subject's participation in the study.
3. Clinically important abnormal laboratory tests.
4. Upper or lower respiratory tract infection of any type within 4 weeks of the first screening visit.
5. Acute exacerbation of IPF within 3 months of the first screening visit.
6. Use of certain medications within 4 weeks of the first screening visit.
7. Receipt of an investigational drug within 6 weeks of the first screening visit.
8. History of cancer of any type in the 5 years preceding the first screening visit, excluding non-melanomatous skin cancer, localized bladder cancer, or in situ cervical cancer.
9. Trauma or surgical procedures requiring hospitalization within 4 weeks of the first screening visit.
10. Planned elective surgery during the study including 4 weeks following the final dose of study drug.
11. History of allergic or anaphylactic reaction to human, humanized, chimeric or murine monoclonal antibodies.
12. Inability to cooperate with study personnel or history of non-compliance to a medical regimen.
13. Previous treatment with FG-3019.

FG-3019 administered at dose of 30 mg/kg (Cohort 2 ) by IV infusion every 3 weeks for 45 weeks in the target population.(first treatment year and first extended treatment year) and every 3 weeks thereafter for three additional extended treatment years.