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Introduction Endothelin-1 (ET-1) acts as a key regulator of vasoconstriction and fibrosis. Many previous studies have focused on the role of ET-1 in SSc. Increased levels of ET-1 are found in SSc endothelial cells and fibroblasts, which correlates with the severity of the fibrotic phenotype.Material and Methods Serum level of endothelin-1 was examined by ELISA and was measured at two points (mean age of patients at the time of inclusion in the study was 49.5±13.1, fem 49(79%), with diffuse form 64,5%, the average follow-up duration was 18.7±14 months. All of the pts underwent HRCT on 1.0-1.5 mm thick overlapping sections using a high-spatial-frequency reconstruction algorithm, which were taken during a single breath hold using various computed tomography scanners. The HRCT images were evaluated by experienced radiologist. HRCT patterns were presence of reticulations, honeycombing, groundglass opacity(GGO). The patients underwent spirometry and measurement of DLCO. Doppler echocardiography was used for detection of mean dates of pulmonary arterial pressure(mPAP).Results At the time and at the end of inclusion in the study mean dates of serum level of ET-1 were(n=64) 126.7±52.4 and (n=45) 159±89.9 accordingly. We didn’t find any correlation with mean dates of FVC, but we found negative correlation of mean level of ET-1 and DLco(R=-0.397 (p<0.05)) At first point and mean level ET-1 at both points with mean dates of DLco at second point (R=-0.395 and R=-0.372 (p<0.05) accordingly). Mean dates of DLco at first and second points were 49.5±18.8 and 49.9±20.8 accordingly. We found correlation between mean dates of FVC and DLco. Also we found negative correlation between mean dates of DLco and mPAP at both points (p<0.05) and direct correlation between mPAP and ET-1 (R=0.428(p<0.05)) at first point. It’s worth noting that mean dates of DLco at first point negative correlated with GGO at both points (R=-0.29 and R=- 035 (p<0.05) accordingly) while ET-1 at the second point directly correlated with GGO also at two points (R=0.484 and R=0.521(p<0.05)). We found correlation ET-1 with mean date of ESR (R=0.45, (p<0.05)), but didn’t find any correlation with CRP.Conclusions The levels of ET-1 in our study negative correlated with DLco, directly with mPAP, ESR and with pattern of ground-glass opacity. This may indirectly confirmed, that scleroderma patients present with high level of ET-1 seem to correlate with the severity of the disease and lung damage. Thus, a decrease in ET-1 during rituximab therapy, may indicate a positive response to therapy.