The effects of continuous and intermittent caffeine abstinence and their time course were investigated under field conditions. After 3 days with habitual coffee, subjects were switched for 9 days to regular instant coffee (n = 40), decaffeinated coffee (n = 40), or an intermittent regime (2 days decaff, 1 day caff, repeated, n = 40). Subjects were blind to the caffeine treatment. Motor activity was assessed continuously; subjective variables, blood pressure (BP), and heart rate (HR) were assessed by the subjects six times per day (electronic diary). Compliance was confirmed by the different caffeine concentrations in daily saliva samples. Continued caffeine consumption showed no effects. Caffeine abstinence resulted in increased HR, decreased motor activity, subjective wakefulness, and well-being, and in increased headaches and use of analgetics. The subjective effects and headaches were transient, i.e., they disappeared after a few days of abstinence and weakened over successive, separated abstinence periods. BP was not affected by the caffeine treatment. The intermittent onset of caffeine consumption resulted in increased wakefulness, whereas the other variables normalized to baseline level.