Study objective Although cellular proliferation is considered one of the dominant processes leading to restenosis following coronary intervention, controversy exists over the extent of cellular replication in atherosclerotic tissue. Accordingly, we sought to investigate the level and clinicopathologic correlates of proliferative activity in atherosclerotic tissue obtained via directional coronary atherectomy (DCA). Design Prospective observational study. Setting Tertiary care referral hospital. Patients Specimens retrieved via DCA from 37 lesions (primary, 26; restenosis, 11) were studied using single-label immunohistochemical staining for the proliferating cell nuclear antigen and basic fibroblast growth factor (bFGF). Results Restenosis tissue was significantly more likely than primary tissue to contain areas of intimal hyperplasia (64 vs 23%; p Conclusion Cellular replication, as measured by expression of the PCNA, occurs in a heterogeneous pattern in both primary and restenotic atherosclerotic tissue obtained from patients undergoing coronary intervention.