ECG monitoring by means of Holter method provides not only information concerning arrhythmias, episodes of ischaemia of the cardiac muscle, but it is also recognised and generally accepted method of investigation of the influence of autonomic system on heart. The aim of the study was to assess the heart rate variability in patients suffering from essential hypertension with different geometry of left ventricle. The studies involved 70 patients, in that 35 women and 35 men (mean age 56.86 +/- 12.3 years). All patients (pts) revealed hypertension, 45 of them mild degree (1 degree), 25 of them moderate degree (2 degrees) according to JNC VI. All patients underwent echocardiography examination, the LV mass was calculated and normalized to the body surface to obtain the LV mass index (LVMI). Based on the LVMI and relative wall thickness (RWT) the type of left ventricle hypertrophy was classified as normal geometry (group 1-17 pts), concentric remodelling (II group--12 pts), concentric hypertrophy (III group--22 pts) and excentric hypertrophy (IV group--20 pts). All of them were submitted to 24-hour Holter monitoring on tape by means of 3-channel registrator MR 45, analysis of ECG tracings was carried out according to Oxfords Optima Jet system. In order to facilitate further analysis, the automatic recording was verified visually and next heart rate variability (HRV) was estimated within 24 hours and separatedly for day hours 6:00-22:00 and night hours 22:00-6:00. CONCLUSIONS: 1. In patients with essential hypertension, hypertrophy and abnormal left ventricular geometry the decrease of parasympathetic activity during day and night hours was observed. 2. The most advanced sympatho-parasympathetic imbalance was noticed in patients with essential hypertension and excentric hypertrophy of left ventricle. 3. The correlations of HRV parameters and LV mass index, the interventricular septum and the left ventricular posterior wall thickness indicate close connection between variables of sympatho-parasympathetic activity and proceeding changes in left ventricle geometry and hypertrophy.