The object of this study was to compare the variability of blood pressure measured non-invasively with the Finapres under resting conditions in hypertensive patients with non-hypertensive subjects matched for age, and to evaluate the relationship between resting blood pressure, i.e. without any stimulation, and the sensitivity of the baroreflex evaluated by crossed spectral analysis (SA). Thirty-four hypertensives (WHO criteria) untreated for three weeks, with a mean age of 50 +/- 7 years, were compared with 60 control subjects with a mean age of 50 +/- 9 years. The blood pressure and heart rate were measured continuously in the dorsal decubitus and standing positions. The direct and crossed SA was undertaken by a specific programme using the fast Fourier method. The average blood pressure of controls differed significantly from that of the hypertensive population (118 +/- 15/65 +/- 10 mmHg vs 157 +/- 20/86 +/- 11 mmHg). The mean heart rate of the hypertensives was faster: 76 +/- 11 vs 67 +/- 10 beats/min (p < 0.001). Under basal conditions, there was greater absolute variability in the hypertensive subjects but the relative variability and heart rate were the same as those of the controls. Direct SA provided additional data by showing that this variability was due to LF oscillations. Crossed SA showed a change in the sensitivity of the slope of regulation of the baroreflex in hypertensives, 7.35 vs 8.68 ms/mmHg (p < 0.05). These results show that, under basal conditions, it is possible to demonstrate an increase in the absolute variability in blood pressure in hypertensive patients.(ABSTRACT TRUNCATED AT 250 WORDS)