The purposes of this study are to assess how the body handles baricitinib when it is given with another drug called probenecid. The study doctor will measure the amount of baricitinib that is absorbed into the blood stream and the time that it takes to remove baricitinib from the body. The safety and tolerability of these drugs will be studied. The study will last about 18 days from the first dose to the end of the study (not including screening).

Inclusion Criteria:

• Male participants: agree to use 2 reliable methods of birth control with female partners of childbearing potential during the study and for at least 3 months following the last dose of study drug
• Female participants: women not of childbearing potential due to surgical sterilization confirmed by medical history or menopause
• Have a body mass index of 18.0 to 29.0 kilograms per meter square (kg/m^2), inclusive
• Have clinical laboratory test results within the normal reference range
• Have normal renal function
• Have normal blood pressure and pulse rate

Exclusion Criteria:

• Are currently enrolled in a clinical trial or are concurrently enrolled in any other type of medical research
• Have completed or discontinued within the last 90 days from a clinical trial involving a study drug
• Are participants who have previously completed or withdrawn from this study or any other study investigating baricitinib, and have previously received baricitinib
• Have known allergies to baricitinib, probenecid, related compounds, or any components of the baricitinib or probenecid formulations, or history of significant atopy
• Have an abnormality in the 12-lead electrocardiogram (ECG)
• Have a history of or current cardiovascular, respiratory, hepatic, renal, gastrointestinal, endocrine, hematological, or neurological disorders capable of significantly altering the absorption, metabolism, or elimination of drugs;
• Have a history of or current gout or gouty arthritis
• Regularly use known drugs of abuse and/or show positive findings on urinary drug screening
• Have a current or recent history of a clinically significant bacterial, fungal, parasitic, viral, or mycobacterial infection
• Have had symptomatic herpes zoster or herpes simplex infection within 90 days prior to the first dose
• Show evidence of human immunodeficiency virus (HIV) infection and/or positive human HIV antibodies
• Show evidence of hepatitis C infection and/or positive hepatitis C antibody
• Show evidence of hepatitis B infection and/or positive hepatitis B surface antigen
• Are women who are lactating
• Intend to use over-the-counter or prescription medication (including salicylate drugs) and/or herbal supplements within 14 days prior to dosing and during the study or intended use of vitamin supplements from first dose of study drug until discharge from the Clinical Research Unit (CRU)
• Have consumed or intend to consume grapefruit or grapefruit-containing products within 7 days prior to the first dose and throughout the study
• Have used or intend to use any drugs or substances that are known to be substrates, inhibitors, or inducers of organic anion transporter (OAT)3 or cytochrome P450 (CYP) 3A4
• Have donated or lost blood of more than 500 milliliter (mL) within the last 3 months
• Have an average weekly alcohol intake that exceeds 28 units per week (males) and 21 units per week (females), or are unwilling to stop alcohol consumption from 48 hours prior to the first dose until discharge from the CRU at the end of study
• History of, in the opinion of the investigator, excessive methylxanthine use within the previous 6 months, such as greater than (>) 6 cups of coffee (or equivalent) per day
• Currently smoke more than 10 cigarettes per day

All enrolled participants.

Baseline through study completion (up to Day 18).