Spontaneous variations of arterial cross section were recorded with impedance rheography (2 MHz) in 20 non-hypertensive subjects and in 23 patients with essential hypertension. The following parameters were measured in both groups: systolic blood pressure (SBP), diastolic blood pressure (DBP), cardiac period (Tc), intrinsic arteria period (Ta) and the ratio of Tc/Ta. Ta and Tc/Ta were significantly different in both groups (p < 0.01). The best discriminant variable was Tc/Ta. When used alone, it yielded an 88 % success in discriminating the subjects of each group. Frequency Fourier analysis showed significant differences between tha harmonic spectra of the two groups. These differences may be due to hypertension itself or to associated hypertension and pathologic disorders of the arterial wall. Their cause and effect relationship with arterial hypertension is discussed.