A multicentre open study to which 229 investigators participated was carried out to demonstrate the safety of cicletanine, a new therapeutic agent, in routine clinical use. Cicletanine was administered alone for three months and normalized blood pressure (less than 160/95 mmHg) in 63 p. 100 of the 1,238 hypertensive patients who entered the study. There was a significant fall of systolic arterial pressure from 178.4 +/- 14.8 to 151.8 +/- 14.2 mmHg and a similar fall of diastolic arterial pressure from 104.0 +/- 6.7 to 86.3 +/- 6.2 mmHg. The reduction of BP values was accompanied by a significant decrease of differential BP (SBP-DBP) from 72.5 to 65.8 mmHg. The initial dosage (50 mg/day) was doubled in only one-third of the patients. The mean daily dose was 66 mg. This antihypertensive effect was paralleled by a significant and major improvement of signs (dyspnoea, oedema of the lower limbs) and symptoms (mainly dizziness, headache, visual and auditory disorders, asthenia) which existed at inclusion. A modest, but significant, reduction of heart rate from 76.7 to 73.9 beats/mn was also noted. Cicletanine produced no toxic or severe adverse events. Clinical side-effects consisted of pruritus, fatigue, headache, vertigo, lower limb oedema and gastrointestinal disorders. These effects were mild and non-specific (doubtful drug imputability); each of them occurred with an incidence ranging from 4.0 to 1.0 p. 100. They were responsible for the withdrawal of about 30 patients (2.4 p. 100). No significant alteration of biochemical or haematological values was recorded.(ABSTRACT TRUNCATED AT 250 WORDS)