['High mobility group box 1 (HMGB1) protein has been identified as a novel pro-inflammatory cytokine in coronary artery disease (CAD). We investigated the relationship between serum HMGB1 level and the severity of coronary artery stenosis.', 'Serum HMGB1 concentration in patients was measured by ELISA. All patients underwent coronary angiography and were assigned into groups according to the quartile of HMGB1 level.', 'HMGB1 level in USAP group was higher than that in control and SAP group. HMGB1 level in SAP group was higher than that in control group (p<0.05). Gensini scores in the highest quartile group (group IV), group III and group II were all significantly higher than that in the lowest quartile group (group I). There was significant correlation between angiographic Gensini score and serum level of HMGB1 (r=0.710, p<0.05). However, in subgroup analysis, we found that serum HMGB1 level was only correlated with angiographic Gensini score in SAP patients (r=0.786, p<0.05), but not USAP patients.'] Is increased serum HMGB1 related to the severity of coronary artery stenosis?