OBJECTIVE Systemic sclerosis (SSc) is accompanied by oxidative stress that in turn may accelerate endothelium degeneration and thus disease progression. We tested whether phagocytes from SSc patients release more reactive oxygen species (ROS) and whether this release correlates with some clinical parameters. METHODS ROS production by blood phagocytes was measured with the luminol enhanced whole blood chemiluminescence (CL). Resting and N-formyl-methionyl-leucyl-phenylalanine -induced CL (fMLP-induced CL) was measured in 30 patients with SSc and 30 healthy controls matched as to age, sex, and level of cigarette smoking. RESULTS Resting CL and fMLP-induced CL calculated per 10(4) phagocytes present in the assayed blood sample were higher in patients with systemic sclerosis than in healthy controls (median; range, 0.88; 0.47-1.39 vs. 0.73; 0.13-1.07 aU/10(4)p and 621; 293-3522 vs. 411; 289-810 aUxs/10(4)p, p<0.02). Patients treated with cyclophosphamide and/or prednisone for 11; 3-168 months did not differ in respect to CL from those that never received the medications. Similarly, no significant differences were found between patients with limited and diffuse SSc. Resting CL correlated (p<0.05) with clinically manifested interstitial lung disease (r=0.59), single breath carbon monoxide diffusing capacity (r= -0.56) and serum autoantibodies titre (r= 0.43). CONCLUSIONS Blood phagocytes from patients with systemic sclerosis, especially from those with interstitial lung disease, generate elevated amounts of ROS as assessed with CL. This confirms the presence of systemic oxidative stress in SSc patients.