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; />=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. (Hypertension 1989;14:563-569) C offee is the most widely used stimulant in Western society. In the Netherlands, 94% of adults drink at least 1 cup/day, and the per capita intake is 4.5 cups/day.1 An increasing proportion of consumers is switching from regular to decaffeinated coffee. In the Netherlands, the market share of decaffeinated coffee grew from 2% in 1984 to 4% in 1987. In the United States, the proportion is already 20%.2 The switch is motivated partly by the well-documented negative effects of caffeine on the quality of sleep and partly by other purported negative effects, including those on the cardiovascular system. However, surprisingly little is known about the actual long-term effect of switching to decaffeinated coffee and how this switch will affect risk factors for coronary heart disease.Epidemiological surveys on the relation between coffee consumption and blood pressure have yielded Supported by Grant 87.026 from the Netherlands Heart Foundation. The coffee was a gift of the Dutch association of coffee toasters and tea packers.Received May 2, 1989; accepted in revised form June 29,1989. contradictory findings.3 -5 Controlled trials showed that in subjects who have abstained from caffeine for a number of days blood pressure rises acutely after a caffeine load. The extent of this acute pressor effect of caffeine depends on the amount and frequency of previous caffeine intake and on the rate of caffeine metabolism; subjects with a high coffee intake appear to be less sensitive to the pressure-elevating effect of caffeine.6 This was confirmed by one experiment that showed no effect of caffeine consumption on blood pressure after 4 weeks 7 ; however, the diet was not controlled, and the power of this trial was small.In the present study...