Experimental and clinical studies have shown that an imbalance of the cardiovascular system autonomous regulation can lead to complications. In this study we have aimed to investigate whether the vegetative control of patients with mild hypertension is disturbed and to evaluate the power of the RR-variability indicators to detect the disturbances. RR variability has been studied in two groups of individuals: normotensive and mildly hypertensive. The indicators of the heart rate variability (HRV) from the 'Cardiovit CS-100 ECG Module' electrocardiograph have been used. The HRV is known to exhibit circadian variations, therefore RR intervals were recorded in two separate sessions: morning (8-9 am) and afternoon (2-3 pm). Each session included three tests: in a resting state, with a handgrip test and with the Valsalva manoeuvre. The multivariate statistical method was applied separately to the morning and afternoon data. A number of classification algorithms were synthesized, yielding correct recognition of normotensive and mildly hypertensive subjects of 91.9% and 94.2% for the morning and afternoon sessions, respectively. We have thoroughly discussed the substantiating reasons for the high statistical significance and reliability of the discrimination obtained. The high sensitivity and specificity of the RR-variability indicators included in the classification models suggest correlative changes of the nervous system vegetative balance in mildly hypertensive patients. The results of the study show the possibility for statistically significant diagnosis of mild hypertension, for prediction of ventricular arrhythmia, left ventricular hypertrophy and ischaemic heart disease.