The Tertatolol International Multicentre Study (TIMS) was aimed at assessing the efficacy and acceptability of 5 mg tertatolol (T) once daily over a 1-year period. The study was carried out in 230 patients (96 men, 134 women, mean age 51.5 ± 0.7 years) with uncomplicated mild-to-moderate hypertension. After a 1-month placebo run-in period followed by a 1-month double blind placebo-controlled period, 213 patients entered and 166 completed the 1-year open period. A diuretic (D) was added if blood pressure (BP) was inadequately controlled with tertatolol alone. After 1 year, 88.5% of patients were controlled (sitting diastolic BP ≤ 90mmHg): 56.3% on single therapy (T) and 32.2% on dual therapy (T + D), respectively. After a 1-month double-blind period, the incidence of emergent symptoms was not significantly different between the placebo group and the tertatolol group. This low incidence was also observed over the 1-year period, side effects leading to the discontinuation of the treatment in 9.1% of the cases. In patients whose creatinine level was initially higher than 100µmol/l, tertatolol significantly decreased creatinine level in the single but not in the dual therapy group. This study confirms that tertatolol is an efficient and well-tolerated antihypertensive drug, which improves renal function.