On study Day 1 after a fast of at least 10 hours, twenty four healthy, non-smoking, non-obese, non-pregnant adult volunteers between the ages of 18 and 45 will be given one oral dose of rosiglitazone (1 x 4 mg tablet). Fasting will continue for 4 hours after the dose. Blood samples will be drawn from all participants before dosing and for 24 hours post-dose at times sufficient to adequately define the pharmacokinetics of rosiglitazone. A 2 day washout period will be completed after the first dose of rosiglitazone on Day 1. On Days 4-7 all subjects will receive a dose of quinine sulfate (2 x 324 mg capsules) every 8 hours starting with the 7:15 a.m. dose on Day 4 and continuing through the 11:15 p.m. dose on Day 7. Doses of quinine sulfate on Days 4-6 will be administered without regard to meals. On the morning of Day 7 after an overnight fast of at least 10 hours, all study participants will receive co-administered doses of rosiglitazone (1 x 4 mg tablet) and quinine sulfate (2 x 324 mg capsules). Fasting will continue for 4 hours after the dose. Blood samples will be drawn from all participants before dosing and for 24 hours post-dose at times sufficient to adequately determine the pharmacokinetics of rosiglitazone. A further goal of this study is to evaluate the safety and tolerability of this regimen in healthy volunteers. Subjects will be monitored throughout participation in the study for adverse reactions to the study drug and/or procedures. Blood pressure (sitting for at least 3 minutes) and pulse will be measured prior to dosing and at 1, 2 and 3 hours after the morning dose of rosiglitazone on Days 1 and 7. Electrocardiograms (EKG) will be recorded on Day 4 before dosing of quinine sulfate and at 1, 2 and 4 hours post-dose and on Day 7 before the co-administered doses of rosiglitazone and quinine sulfate and at 1, 2 and 4 hours post-dose. All adverse events whether elicited by query, spontaneously reported, or observed by clinic staff will be evaluated by the investigator and reported in the subject's case report form.