The smoking and drinking habits of 58 patients with accelerated hypertension were compared with those of a control group of 58 patients with benign hypertension, each individually matched for age, sex and date of presentation. Thirty-eight (66 percent) of the patients with accelerated hypertension were regular smokers compared to 26 (45 percent) of the control group. This excess of smokers was significant, but the average number of cigarettes smoked by smokers in the two groups was similar. The number of patients known to consume alcohol was the same in the two groups; and there were no significant differences in amount of alcohol drunk. Smoking and alcohol habits were not related. Thirty-six patients (62 percent) with accelerated hypertension had serum creatinine levels greater than 0.12 mmol/l compared with nine (16 percent) of the control group. Seventeen (29 percent) patients with accelerated hypertension were known to have died compared with five (9 percent) of the control group. This survey confirms that, as shown by recent studies in Britain, smoking is more common in patients presenting with accelerated than with benign hypertension. It appears that hypertensive patients who smoke regularly are more likely to develop the accelerated phase than those who do not.