There is a strong association between cigarette smoking and accelerated hypertension. In mild hypertension smoking cigarettes has a distinct presser effect and caffeine a small but more prolonged presser action. Coffee and cigarette smoking together have an additive effect on blood pressure (BP). We have examined the interaction of cigarette smoking and drinking coffee on the BP of six patients who presented with accelerated hypertension (mean BP 240/140 mm Hg) and were heavy smokers and caffeine users. After initial control of the BP, the effects of smoking alone, coffee plus smoking, and placebo were examined in a balanced cross-over study. Baseline BP averaged 154/91 mmHg and remained stable for 90 min after abstention from smoking and caffeine (placebo). Cigarette smoking without caffeine caused a modest rise in BP (mean 9/8 mm Hg), but the combination of coffee plus cigarette smoking caused a progressive increase in BP to an average 21/17 mm Hg (P < 0.05/P < 0.002) higher than placebo values. The effect of coffee was significantly additive to that of smoking alone. Smoking plus coffee ingestion shifted the BP from acceptable (155/94 mm Hg) to poor control (175/107 mmHg). This presser effect was observed despite treatment, and with amounts of caffeine and cigarettes which were in no way unusual for these patients. We propose that the association of cigarette smoking with accelerated hypertension may reflect an extreme presser effect of combined smoking and caffeine use in some patients.