The effect of decaffeinated versus regular coffee on blood pressure and heart rate was investigated. In a randomized double-blind, crossover trial, 45 healthy volunteers (23 women and 22 men, 25-45 years old) with a habitual intake of 4-6 cups coffee/day received 5 cups of regular coffee each day for a period of 6 weeks, and 5 cups of decaffeinated coffee for the next 6 weeks or vice versa. The background diet was kept constant. The total amount of caffeine ingested was 40 mg during the decaffeinated coffee period and 445 mg during the regular coffee period. Use of decaffeinated coffee led to a significant but small decrease in systolic (mean +/- SEM, -1.5 +/- 0.4 mm Hg; p = 0.002) and diastolic (-1.0 +/- 0.4 mm Hg; p = 0.017) ambulant blood pressure and to a small increase in ambulant heart rate (+1.3 +/- 0.6 beats/min; p = 0.031). Individual differences in rate of caffeine metabolism did not explain differences in long-term response of blood pressure to caffeine. We conclude that in normotensive adults replacement of regular by decaffeinated coffee leads to a real but small fall in blood pressure. However, it remains to be established whether a mass switch from regular to decaffeinated coffee would significantly reduce the total incidence of hypertension-related disorders.