1. Patients with mild hypertension who habitually smoked cigarettes and consumed caffeine were examined after abstaining from caffeine and cigarettes overnight. Their mean blood pressure (147/89 mmHg) was substantially lower than values recorded in the clinic (164/102 mmHg) and remained so when they continued to abstain (149/94 mmHg at 2 h).
2. Smoking two cigarettes (3.4 mg of nicotine) elevated blood pressure by 10/8 mmHg but for only 15 min.
3. Drinking coffee (200 mg of caffeine) elevated blood pressure by up to 10/7 mmHg between 1 and 2 h.
4. Combined coffee and cigarette smoking caused a sustained rise in blood pressure from 5 to 120 min to levels similar to those measured in the clinic (162/102 mmHg at 2 h). The interaction of coffee and cigarettes on blood pressure, but not on pulse rate, was significant.
5. Caffeine ingestion with or without smoking may be important in the genesis of mild hypertension.