Aim To investigate the expression and significance of interleukin-18 and matrixmetalloproteinase-9 in human coronary arteries with different atherosclerotic lesions.Methods 48 coronary arteries specimens from 14 autopsy cases were divided into 3 different groups according to HE staining,which were unstable plague group,stable plague group and normal group.These specimens were detected by immunohistochemistry and reverse transcription-polymerase chain reaction for protein and mRNA analysis.Results Interleukin-18 and matrixmetalloproteinase-9 mRNA and protein expression can be detected in atherosclerosis,and there is significant difference between unstable plaques and stable plaques.The levels are significantly higher in unstable plaques.Positive association between interleukin-18 and matrixmetalloproteinase-9 expression intensity showed in Spearman tests.Conclusions These results indicates interleukin-18 and matrixmetalloproteinase-9 both participate in the initiation and development of atherosclerosis and are highly relevant to the unstable plaque.These findings suggests that interleukin-18 is in coordination with matrixmetalloproteinase-9 during the development of atherosclerosis.