Inclusion Criteria:

Double blind study phase:

1. Males or females (not nursing and not pregnant), at least 18 years of age. Women of
child bearing potential (WOCBP) are eligible if they are practicing effective
contraceptive measures

2. Subjects must meet the criteria of the American Rheumatism Association (1987) for the
diagnosis of rheumatoid arthritis and the American College of Rheumatology (1991)
functional classes I, II, or III

3. Subjects have been taking Methotrexate (10-30 mg weekly) for at least 6 months, and
at a stable dose for 28 days prior to treatment

4. Washout/drug stabilization requirements (except Methotrexate) [Informed consent must
be signed before making any changes in RA therapy if those changes are solely for the
purpose of this study].

- Leflunomide or Infliximab have already been discontinued at least 60 days prior
to enrollment (prior to signing of informed consent) and a total of 90 days
prior to treatment. All other Disease Modifying Anti-Rheumatic Drugs (DMARDs)
(except Methotrexate) have been withdrawn at least 28 days prior to treatment

- Oral corticosteroid treatment has been reduced to the equivalent of 10 mg or
less prednisone daily and stabilized for at least 28 days prior to enrollment

5. Eligibility of subjects for the study is based on their disease activity and
anti-rheumatic treatment at the initial visit:

- Methotrexate monotherapy: Subject is receiving only Methotrexate, steroids,
Non-steroidal anti-inflammatory drugs (NSAIDs) and will not require washout

- Combination therapy: Subject is receiving Methotrexate in combination with
another DMARD(s) and will require washout

At entry, Methotrexate monotherapy must have a disease activity:

- 10 or more swollen joints (66 joint count)

- 12 or more tender joints (68 joint count)

- C reactive protein (CRP) ≥.1 mg/dL (10 mg/L) at "Screening" visit

At entry, combination therapy must have a disease activity (if subject does not
satisfy the above):

- 6 or more swollen joints (66 joint count)

- 8 or more tender joints (68 joint count)

- No restriction on C-reactive protein (CRP)

In addition

All subjects who were on combination therapy at entry must undergo a 28 day washout
period of DMARDs other than Methotrexate. After the washout/drug stabilization and
prior to randomization such subjects must have:

- 10 or more swollen joints (66 joint count)

- 12 or more tender joints (68 joint count)

- C reactive protein (CRP) ≥ 1 mg/dL (10 mg/L)

6. Subject is willing to participate in the study and willing to sign the informed
consent

Open label study phase:

- Participants that have completed the initial short term portion (double blind) of the
study

Exclusion Criteria:

Double blind study phase:

1. Subjects who have at any time received treatment with BMS-188667 (Abatacept)

2. Subjects who within 30 days of the Day 1 visit have received treatment with any
investigational drug

3. Subjects with active vasculitis of a major organ system (except for subcutaneous
rheumatoid nodules)

4. Current symptoms of severe, progressive, or uncontrolled renal, hepatic,
hematological, gastrointestinal, pulmonary, cardiac, neurological, or cerebral
disease. Concomitant medical conditions that in the opinion of the investigator might
place the subject at unacceptable risk for participation in this study

5. Mammogram requiring further investigation or biopsies leading to the diagnosis of a
clinically significant abnormality. Complete evaluation of lesion is required before
initiation of dosing

6. Subjects with a history of cancer within the last five years (other than non-melanoma
skin cell cancers cured by local resection)

7. Subjects who have a history of clinically significant drug or alcohol abuse, or admit
to consumption of more than 1 alcoholic drink per day

8. Subjects with evidence (as assessed by the investigator) of active or latent
bacterial or viral infections at the time of potential enrollment, including subjects
with evidence of Human Immunodeficiency Virus (HIV) infection, or hepatitis B or C
infection

9. Subjects with any serious or chronic infections such as pneumonia, pyelo-nephritis,
renal infection, chest infection with bronchiectasis, or sinusitis in the previous 3
months

10. Subjects with active tuberculosis requiring treatment within the previous 3 years

11. Subjects with any opportunistic infections such as herpes zoster or cytomegalovirus
(CMV) within the previous 2 months

12. Subjects with severe asthma defined as > 3 emergency room admissions in the last year
or > 3 treatments with oral steroids for asthma in the last year

13. A history of either angioedema or anaphylaxis that was associated with a reaction to
a drug

14. Subjects with the following laboratory values:

- Hemoglobin < 8.5 g/dL

- White blood cells < 3000/mm3

- Platelets < 100,000/mm3

- Serum creatinine > 2 times upper limit of normal

- Serum Alanine aminotransferase (ALAT) or Aspartate aminotransferase (ASAT) > 2
times upper limit of normal

- Any other lab values that in the opinion of the investigator might place the
subject at unacceptable risk for participation in this study

Open label study phase:

- Participants must continue to meet inclusion/exclusion criteria as in the short term
(double blind) phase of the protocol except subjects who have receiving other than
Abatacept