Heart rate variability (HRV), hemodynamics, cerebral alpha-rhythm and systemic relations between them were investigated in 35 normal human subjects at the age of 37.2 +/- 3.8 years. Results of comprehensive clinical, functional and instrumental HRV investigations, electroencephalography (EEG) using 21 monopolar electrodes and blood pressure (BP) monitoring were embodied in mathematical models describing the relations of these parameters, multiple regression equations, and generated 3-D diagrams. It was found that relative increase of LF and reductions of HF ranges occurred on the background of BP elevation. The EEG alpha amplitude was depressed and alpha index decreased. The HRV reduction and modification of the alpha-rhythm structure were demonstrated to affect BP values. These data point to interactions and tight relations between the vegetative and central nervous systems and BP.