In 15 centres of the Czech Republic the antihypertensive effect of Amlodipine-Norvasc of Pfizer Co. was tested in 155 patients with mild or medium severe hypertension. The patients were treated by monotherapy, using doses of 5 mg (92%) and 10 mg (8%) per day. In all investigated hypertensive subjects a statistically significant decline of the systolic and diastolic blood pressure occurred in the course of the 12-week investigation (P smaller than 0.01) without affecting the heart rate. The rate of undesirable effects of treatment was very low: only three patients (1.9%) discontinued treatment on account of undesirable effects. The most frequent ones included perimalleolar oedema, the sensation of fullness, headache, cardiac palpitations, vertigo and insomnia. Evaluation of the antihypertensive effectiveness and tolerance of the preparation by the physician and patient is positive, and Amlodipine-Norvasc of Pfizer Co. holds therefore, because of its pharmacokinetic and pharmacodynamic properties, an important place among calcium channel inhibitors of the second generation.