Background: Serum lipids and inflammatory markers have been associated with the pathogenesis of atherosclerosis and acute coronary syndromes (ACS). However, no association has been reported between the levels of these markers and the IVUS characteristics of culprit plaques (CPs) in ACS. Previously, we have demonstrated that CPs show distinct IVUS characteristics, namely thinner fibrous caps, larger plaque areas and burdens, higher indices for remodelling and eccentricity, and lower mean grayscale level (MGL) and grayscale variance, reflecting a predominance of echolucent tissues, when compared to non-culprit plaques. This study aims at examining the relation between the levels of serum lipids, interleukin-6 (IL-6) and C-reactive protein (hsCRP), and the IVUS characteristics of CPs in ACS. Methods: IVUS examination was performed on 30 angiographically identified CPs (18 patients with post-MI angina and 12 with unstable angina) by motorized pullback of the transducer in the culprit vessel at 0.5 mm/s. The IVUS images were digitized during acquisition at 10 frames/s to preserve image quality and resolution and were analysed offline. The frame with the smallest lumen area was used to calculate plaque area, lesion plaque burden, reference plaque burden, minimum thickness of the fibrous cap, remodelling index and the eccentricity index. Computer-assisted measurements of grayscale parameters included the MGL, variance and contrast. Blood samples were taken immediately prior to the IVUS run for estimation of the serum levels of total cholesterol (Chol), LDL, HDL, triglycerides (TG), CRP, and IL-6.Results: Chol and LDL showed a positive correlation only with the mean reference plaque burden (r=0.51, p=0.004 and r=0.57, p=0.001 respectively) and no other IVUS parameters. HDL and TG showed no significant correlations. IL-6 (median level 16.8 pg/ml) showed a significant positive correlation with the remodelling index (1.07±0.2; r=0.44 p=0.015) as well as a negative correlation with MGL (14.4±3.0; r=-0.44, p=0.014), variance (22.7±6.8; r=-0.55, p=0.002) and contrast (62.8±18; r=-0.43, p=0.019). CRP was not correlated with any IVUS parameter. Conclusion: Chol and LDL were correlated with the extent of atherosclerosis of the culprit vessel but not with the characters of the CP. IL-6 correlated with most IVUS characteristics of the CP possibly supporting current evidence of production of IL-6 in the CPs. The relatively late production of CRP in the inflammatory cascade might explain its lack of correlation with CP