Blood pressure in some elderly hypertensive patients is characterized by marked lability. This affects quality of life and may deteriorate prognosis. Conventional anti-hypertensive medication does not lead to stabilization of blood pressure. We call this form of hypertension "labile hypertension of the elderly" (LHE). The aim of the study was investigation of autonomic regulation of blood pressure and of clonazepam effectiveness in patients with LHE. Fifty-six patients with LHE (mean age 67.0 +/- 6.3 years) entered the study (87.5% women). Control group consisted of 38 patients with stable hypertension and 27 normotensives matched by sex and age. The patients and the controls underwent clinical and psychological examinations, regular measurement of blood pressure during one month before and after the treatment, cardiovascular tests and spectral analysis of the heart rate variability. It was found that LHE patients have higher level of anxiety and depression, low standard deviation of RR interval, low normalized LF and HF components and increased normalized VLF component. The cardiovascular tests showed signs of diminished parasympathetic regulation. Clonazepam treatment in a dose 1-2 mg/day brought about a significant stabilization of blood pressure in 82.0% of patients with LHE. Thus, LHE is an original form of hypertension in patients over 60 years old characterized by frequent, short-term, small symptomatic, spontaneous fluctuations of blood pressure with development of both hypertensive and hypotensive reactions. Pathogenesis of LHE is linked with disorders of heart rate autonomic regulation, marked anxiety and depression. Clonazepam stabilizes blood pressure in most LHE cases.