Objectives To test whether serum level of matrix metalloproteinase (MMP)-9 is associated with the development of in-stent restenosis (ISR) in patients treated with drug-eluting stents (DES).

Methods 120 patients who were treated with DES were enrolled into our study. Blood samples for measurement of MMP-9 antigen and activity were taken directly before and 48h after percutaneous coronary intervention (PCI). Restenosis was evaluated at 9–12 months by coronary angiography.

Results During the follow-up period, 1 patients (0.8%) died of cardiovascular causes, and 7 patients (5.8%) developed angiographic ISR. Patients with ISR showed significantly higher serum activity of MMP-9 at baseline (p < 0.01) and after the procedure (p < 0.01). The PCI increased serum activity of MMP-9 (p = 0.008) only in patients with ISR.

Conclusions Elevated serum activity of MMP-9 is associated with dramatically increased restenosis rates after PCI with implantation of DES. Assessment of MMP-9 level might be useful for identification of patients who are at high risk for ISR despite implantation of DES.