Tertatolol has been studied in 2,338 patients with mild to moderate hypertension over a one year period. Tertatolol (T) was initiated alone (5 mg once daily) and if satisfactory control of blood pressure (BP) (diastolic BP less than 95 mm Hg) was not achieved, treatment was adapted at the third or sixth month either by increasing the dosage (heart rate greater than 70 beats/min), or by adding a potassium-sparing diuretic (heart rate less than or equal to 70 beats/min). Blood pressure normalization was achieved in 88.8% of the study population: 66.1% on single and 22.7% on dual therapy. The decrease of diastolic BP was 18.4 mm Hg (from 102.8 +/- 0.2 to 84.4 +/- 0.2 mm Hg, P less than .001). Tertatolol alone or associated with diuretic (T + D) induced a significant and continuous decrease in supine systolic and diastolic BP. Overall side effects were rare, leading in only 6.5% of the cases to the discontinuation of the drug. Plasma creatinine significantly decreased in the single therapy group only (from 92.2 +/- 0.5 to 90.1 +/- 0.5 mumol/L, P less than .01). In patients with initial plasma creatinine greater than or equal to 100 mumol/L (n = 661), plasma creatinine markedly decreased (-10%, from 114.6 +/- 0.7 to 103.4 +/- 0.8 mumol/L, P less than .01), and to the same extent with T or T + D. Thus, this large-scale study confirms that tertatolol is an efficient and well-tolerated antihypertensive drug, which improves renal function, especially when initially reduced.