In this study, a 10 mg tasocitinib (CP-690,550) tablet will be administered to healthy subjects on two separate dosing occasions. On one occasion the tasocitinib (CP-690,550) tablet will be administered in a fasting condition; On the other occasion the tasocitinib (CP-690,550) tablet will be administered in a fed condition following a standard breakfast meal. The amount of tasocitinib (CP-690,550) in the blood will be measured at various times over 24 hours following each dosing occasion and compared to evaluate for any differences.

To evaluate the effect of food on the pharmacokinetics of tasocitinib (CP-690,550).

Inclusion Criteria:

• Healthy male and/or female (non-childbearing potential) subjects between the ages of 21 and 55 years.
• Body Mass Index (BMI) of 17.5 to 30.5 kg/m2; and a total body weight for males>50 kg (110 lbs). For females, total body weight >45 kg (99 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.
• Evidence or history of any clinically significant infections within the past 3 months.
• Use of tobacco- or nicotine-containing products in excess of the equivalent of 5 cigarettes per day.