In a single-blind study the effects of drinking two cups of regular or decaffeinated coffee on blood pressure, heart rate, forearm blood flow and plasma concentrations of caffeine, renin and catecholamines were studied in 12 normotensive subjects. Drinking regular coffee led to a rise of blood pressure, a fall of heart rate and an increase of plasma catecholamines. Decaffeinated coffee induced a smaller increase of diastolic blood pressure without changing other parameters. This study shows that the cardiovascular effects of drinking coffee are mainly the result of its caffeine content.