Power spectral analysis (PSA) of heart rate (HR) and blood pressure (BP) may provide useful informations about neural control of the cardiovascular system. Aim of the study was to evaluate PSA of HR and BP in a group of normal subjects (N) and hypertensive patients (H), with and without left ventricular hypertrophy (LVH), in the following situations: 1) at rest, in the morning and also at different hours during the day and night, 2) during application of a negative pressure (LBNP) to the lower body, in order to induce sympathetic activation. PSA of HR was performed on sequences of 512 beats, in a total number of 12 N, 19 H without LVH, 20 H with LVH. In 10 of the subjects PSA of BP variability was also performed. Absolute and normalized power spectral density (PSD) of the peaks at 0.10 (low frequency peak = LF) and at 0.25 (high frequency peak = HF) Hz, as well as their ratio (index of sympathovagal interaction: SVI) were calculated. H with LVH had a SVI index significantly higher in respect to that found in N and in H without LVH (p<0.05); in addition, SVI index was significantly less during night in N and in H without LVH, compared to H with LVH (p<0.05). In the group of H with LVH, changes in SVI during LBNP were markedly reduced. In the group of patients studied so far, results of PSA of BP were similar to those obtained performing PSA of HR, thus suggesting an increased sympathetic drive to the heart, and, probably, also to the vasculature, in H with LVH.