Background:Programmed cell death-1 (PD-1) is an immunoreceptor that negatively regu-lates antigen receptor signaling and plays a critical role in the immunoregulation of autoimmune diseases.Aim of the work:This study aimed to measure the plasma and synovial fluid levels of soluble pro-grammed death-1(sPD-1) in rheumatoid arthritis (RA) patients and to correlate them with the clinicaland laboratory characteristics, disease activity, functional status and radiological severity.Patients and methods:We measured sPD-1 in the plasma (n= 60) and synovial fluid (SF) samples(n= 24) from 60 RA patients and in the plasma from healthy control (n= 30). In the patients, dis-ease activity score using 28 joint counts (DAS28) and the health assessment questionnaire (HAQ)score were assessed; immunoglobulin-M rheumatoidfactor (IgM-RF) titer, anti-cyclic citrullinatedpeptide (anti-CCP) antibodies titer and C-reactive protein (CRP) levels were measured and total Sharpscore calculated.Results:In RA patients both plasma and SF sPD-1 levels (1416.9 ± 1037.9 pg/ml and1503.9 ± 1129.48 pg/ml respectively)were highly significantly increased compared to its plasma levelin the healthy control (165 ± 26.11 pg/mL) (p< 0.001). In RA patients, the plasma and SF levels ofsPD-1 significantly correlated with DAS28 (r= 0.52 and 0.58 respectively,p