Background: We hypothesized that patients with coronary atherosclerosis have increased plasma levels of cathepsin S (CATS) and cathepsin B (CATB) mRNA, the genes that are involved in atherosclerotic plaque development and destabilization. Methods: mRNAs were isolated from plasma of 67 patients with coronary atherosclerosis (29 with stable angina, 38 with acute coronary syndrome) and 33 healthy subjects as controls, transcribed to cDNA and quantified by real-time PCR. Results: Plasma levels were successfully measured in all samples. Patients with coronary atherosclerosis had 2.75 times higher plasma levels of CATS mRNA than controls (median 6.10 vs. 2.22; pb0.001). No difference was observed in CATB mRNA levels (median 5.62 vs. 6.19; p=0.866). Patients on therapy with statins and aspirin tended to have higher plasma levels of CATS mRNA than patients without statins and aspirin (median 6.41 vs. 4.27; p=0.028). Conclusions: Further evaluation of plasma CATS mRNA levels in patients with coronary atherosclerosis is reasonable.