Monocytes have been shown to take an important role in collateral growth in animal studies. The aim of the study was to investigate the relation of circulating monocyte count with collateral development in patients with severely stenotic CAD. Patients who had >= 95% stenosis in at least one major coronary artery were included in the study. Coronary angiograms of 210 eligible patients from our database were analyzed again and 103 of them had good and 107 had poor collateral development according to Cohen-Rentrop method. Only the monocyte count was found to be significantly different between two groups (671 +/- 218 mm(-3) versus 522 +/- 195 mm(-3), p < 0.001) when multivariate analysis was performed and an increased monocyte count was observed in the good collateral group (Odds ration [OR], 2.918; 95% confidence interval [CI], 1.281-6.648,p = 0.011). This study in which the relationship between monocyte count in blood and collateral development was disclosed has a potential importance in clinical and basic cardiovascular medicine. (c) 2007 Elsevier Ireland Ltd. All rights reserved.