In this study, a 10 mg dose of CP-690,550 will be given to study subjects on two separate occasions by two different routes of administration: One time by mouth in tablet form and one time by vein (intravenous form). The amount of CP-690,550 available in the blood following administration by vein will be measured and is expected to reflect the maximum amount possible for the 10 mg CP-690,550 dose. The amount of CP-690,550 that is achieved in the blood following oral tablet administration will also be measured and compared to that achieved following administration by vein in order to estimate how much of the maximum amount possible is actually absorbed into the blood following administration by mouth as a tablet.

To estimate the absolute bioavailability of a 10 mg oral dose of tasocitinib (CP-690,550) compared to a 10 mg intravenous dose of tasocitinib (CP-690,550) in healthy subjects.

Inclusion Criteria:

• Healthy male and/or female (non childbearing potential)
• Subjects between the ages of 21 and 55 years, inclusive
• Body Mass Index (BMI) of 17.5 to 30.5 kg/m2; and a total body weight >50 kg (110 lbs)
• No evidence of active or latent or inadequately treated infection with Mycobacterium tuberculosis (TB)

Exclusion Criteria:

• Evidence or history of any clinically significant illness, medical condition, or disease.

  2. Evidence or history of any clinically significant infections within the past 3 months.

  3. Use of tobacco- or nicotine-containing products in excess of the equivalent of 5 cigarettes per day.