A sedentary workforce may be at increased risk for future cardiovascular disease. Exercise at the work site has been advocated, but effects on endothelium as a biomarker of risk and relation to weight loss, lipid changes, or circulating endothelial progenitor cells (EPCs) have not been reported. Seventy-two office and laboratory employees (58 women; average age 45 years, range 22 to 62; 26 with body mass index values >30 kg/m(2)) completed 3 months of participation in the National Heart, Lung, and Blood Institute's Keep the Beat program, with the determination of vital signs, laboratory data, and peak oxygen consumption (VO(2)) during treadmill exercise. Brachial artery endothelium was tested by flow-mediated dilation (FMD), which at baseline was inversely associated with Framingham risk score (r = -0.3689, p <0.0001). EPCs were quantified by colony assay. With exercise averaging 98 +/- 47 minutes each workweek, there was improvement in FMD (from 7.8 +/- 3.4% to 8.5 +/- 3.0%, p = 0.0096) and peak VO(2) (+1.2 +/- 3.1 ml O(2)/kg/min, p = 0.0028), with reductions in diastolic blood pressure (-2 +/- 8 mm Hg, p = 0.0478), total cholesterol (-8 +/- 25 mg/dl, p = 0.0131), and low-density lipoprotein cholesterol (-7 +/- 19 mg/dl, p = 0.0044) but with a marginal reduction in weight (-0.5 +/- 2.1 kg, p = 0.0565). By multiple regression modeling, lower baseline FMD, greater age, reductions in total and low-density lipoprotein cholesterol and diastolic blood pressure, and increases in EPC colonies and peak VO(2) were jointly statistically significant predictors of change in FMD and accounted for 47% of the variability in FMD improvement with program participation. Results were similar when modeling was performed for women only. In contrast, neither adiposity at baseline nor change in weight was a predictor of improved endothelial function. In conclusion, daily exercise achievable at their work sites by employees with sedentary occupations improves endothelial function, even with the absence of weight loss, which may decrease cardiovascular risk, if sustained.