Background Vasoactive factors have been reported to correlate with vulnerable plaque and acute coronary syndrome (ACS). This study aimed to investigate the relationship between vasoactive factors and plaque morphology in patients suffering from non-ST-segment elevated ACS. Methods From April 2007 to April 2009, 124 consecutive patients suffering from non-ST-segment elevated ACS who had received coronary angiography (CAG) and intravascular ultrasound (IVUS) in the People's Liberation Army General Hospital and Beijing Anzhen Hospital were enrolled in this study. Three serum vasoactive factors, plasma soluble vascular endothelial growth factor receptor-1 (sFlt-1), placental growth factor (PLGF) and interleukin-18 (IL-18), were measured by enzyme-linked-immunosorbent serologic assay of the patients. The levels of vasoactive factors were compared between vulnerable plaque group and stable plaque group, and between unstable angina pectoris (UAP) group and non-ST-segment elevation acute myocardial infarction (NSTE-AMI) group. The relationship between the plaque morphology and levels of vasoactive factors was analyzed. Results The levels of vasoactive factors were similar between the UAP group (69 patients) and NSTE-AMI group (55 patients). The levels of sFlt-1 and PLGF in the vulnerable plaque group were significantly higher than those in the stable plaque group. The level of IL-18 was correlated positively with plaque morphology. Multivariate Logistic regression analysis showed that the level of PLGF was an independent risk factor for vulnerable plaque (OR=2.115, 95%Cl 1.415-5.758, P=0.018). Using the ROC curve, PLGF was a significant factor for the diagnosis of vulnerable plaque (the diagnostic point was 26.3 ng/L, the proportion of square area under the ROC curve was 0.799, 95%Cl 0.758-0.839, P <0.001; the sensitivity of PLGF under the ROC curve was 86%, and the specificity 63%). Conclusion Both IL-1 8 and PLGF are biomarkers for vulnerable plaques and helpful to predict vulnerable plaque. Chin Med J 2010;123(2):193-197