The ankle-brachial systolic pressure index (ABI), a noninvasive measure of peripheral arterial occlusive disease (PAOD) severity, is considered a marker of atherosclerosis and an independent predictor of mortality. However, it is not known whether factors other than PAOD severity, such as cigarette smoking, have an effect on ABI measurement. Therefore, the authors examined the acute effects of cigarette smoking on ABI and the peripheral circulation in 10 older (63 ±10 years) chronic smokers (39 ±37 pack-years) with PAOD (ABI=0.64 ±0.14). The patients were instructed to refrain from smoking and from consuming caffeine-containing beverages for at least 12 hours before the tests. The patients were randomly assigned to 2 days of testing consisting of a nonsmoking and a smoking day. Resting heart rate, blood pressure, ABI, and calf blood flow by plethysmography were obtained on both testing days. The smoking day consisted of smoking two filter cigarettes over a period of 10 minutes before the measurement of ABI and calf blood flow. The ABI on the smoking day (0.55 ±0.11) was lower (p=0.008) than on the nonsmoking day (0.64 ±0.14) owing to a lower (p=0.020) ankle systolic blood pressure (81 ±28 vs 93 ±28 mmHg). Brachial systolic blood pressures, heart rate, and calf blood flow were not altered by smoking (p>0.05). These results demonstrate that the acute effect of cigarette smoking lowers the ABI in chronic smokers with intermittent claudication, thereby yielding evidence of a transient deleterious effect of cigarette smoking on the peripheral circulation in chronic smokers.