1 In a double-blind crossover trial, the effect of 4 week daily ingestion of eight cups of regular coffee (corresponding to 504 mg caffeine) vs eight cups of decaffeinated coffee was studied. Blood pressure, heart rate and urinary catecholamines were measured in eight healthy, young volunteers. 2 In both groups, regular coffee immediately led to a significant increase in mean blood pressure (+ 3 and + 5 mm Hg respectively). The difference between both groups, however, existed only in the first 3 to 5 days of ingestion of regular coffee. On day 5 after ingestion of regular coffee, and thereafter in weekly intervals, no significant increase in catecholamine excretion was observed. 3 The data suggest that long-term consumption of large amounts of coffee leads to only a small and transient rise in mean blood pressure. This may be due to an adaptation phenomenon. 4 Therefore, continuous heavy coffee ingestion (eight cups/day for 4 weeks) by young persons does not appear to involve a risk of the development of hypertension.