Although smoking raises blood pressure, the office blood pressure measurements of smokers are the same as, or lower than, those of nonsmokers. To resolve this paradox, we compared the office and 24-hour ambulatory blood pressures of 59 untreated hypertensive smokers with 118 nonsmoking hypertensives matched for age, sex, and race. The office blood pressures of the smoking and nonsmoking groups were 141/93 and 142/93 mm Hg, respectively. The awake ambulatory systolic blood pressure was significantly higher in the smokers (145 vs 140 mm Hg). This difference was greater among patients over the age of 50 years (153 vs 142 mmHg), and absent among patients under 50 years (140 vs 139 mm Hg). Blood pressures during sleep did not differ between the two groups (121/76 vs 123/77 mm Hg). We conclude that, among white hypertensives above the age of 50 years, smokers maintain a higher daytime ambulatory systolic blood pressure than nonsmokers even though blood pressure measured in the office is similar.