In a double-blind, within-patient study, blood pressure was measured at regular intervals at the clinic by the physician and each day at home by the patient. Both methods of blood pressure measurement demonstrated an antihypertensive effect of the diuretics chlorthalidone (25 mg) and triamterene (50 mg) and the β-blocker oxprenolol (160 mg) and the greater efficacy of the combination of the two therapies. During placebo, as well as during active treatment, blood pressure values were higher at the clinic than at home, except when the patients were taking the β-blocker, which minimized the arousal response during blood pressure measurements in the clinic. With 2-week treatment periods, separated by 2 weeks of placebo administration, blood pressure returned toward its initial level after each of the three treatments and none of the carryover effects was significant at the 5% level. This methodology was intended to make it possible to demonstrate in 27 patients at the clinic and in 20 patients with measurements made at home, at the usual statistical risks (α=5%, β=10%), a fall of 5 mm Hg in diastolic blood pressure in comparison with a placebo. Moreover, at the end of this 3-month follow-up, each patient could continue to receive the treatment that was the most effective and the best tolerated. In conclusion, the use of a within-patient trial design, with a 15-day washout period between active treatments and careful recording of blood pressure values, can minimize the number of patients included in hypertension trials and offer to each patient the possibility of individualization of treatment.