Coffee consumption has been weakly linked to high blood pressure (BP). The hypothesis that cessation of caffeinated-coffee consumption lowers ambulatory BP was tested in men in a randomized trial. One hundred eighty-six middle-aged, normotensive, male, habitual caffeinated-coffee consumers were recruited. Of these subjects, 150 had sufficiently complete, ambulatory BP measurements for analysis. After 2 months of standard caffeinated-coffee consumption, subjects were randomized to consume an equal amount of the same standard caffeinated coffee or a standard decaffeinated coffee, or to discontinue coffee consumption for 2 months. Diet composition, body weight and exercise did not change. Resting BP and heart rate were not different between the groups before and after intervention. In comparison with the continued caffeinated-coffee group (control), the decaffeinated-coffee group revealed significant reductions in mean ambulatory systolic BP during the morning (-4.0 +/- 11 mm Hg; p = 0.014), afternoon (-5.3 +/- 10 mm Hg; p = 0.001) and evening (-3.2 +/- 10 mm Hg; p = 0.003) hours, reductions in mean ambulatory diastolic BP during the afternoon (-1.8 +/- 10 mm Hg; p = 0.063) and evening (-1.8 +/- 10 mm Hg; p = 0.059) hours and no change in ambulatory heart rate.(ABSTRACT TRUNCATED AT 250 WORDS)