Spectral analysis was recently chosen to characterize the fast oscillations, depending on the autonomic nervous system, in heart rate and blood pressure variabilities. Humoral stimuli could impinge on the low-frequency domain of blood pressure variability since the time lag to humoral system activation is greater. This study was designed to analyse low-frequency components of short-term variability of blood pressure of conscious rats in conditions where humoral systems were activated. We studied rats with two-kidney, one-clip Goldblatt hypertension in which the blood pressure level was dependent upon the renin-angiotensin and kallikrein-kinin systems. Spectral powers of the systolic and diastolic blood pressure and heart rate were computed in the high (respiratory)-, mid (0.2–0.6 Hz)- and low (0.02–0.2 Hz)-frequency bands, as detected by the fast Fourier transform technique in consecutive 102-s stationary periods. Hypertensive rats exhibited a marked low-frequency component of systolic (+ 261%) and diastolic (+ 169%) blood pressure variabilities when compared to sham-operated animals. First, losartan, a selective non-peptide angiotensin AT 1 receptor antagonist, reduced this low-frequency component (− 44% and − 25% for systolic and diastolic blood pressure). In a second series of hypertensive rats, HOE 140, d-Arg-[Hyp 3,Thi 5, d-Tic 7,Oic 8]bradykinin, a bradykinin B 2 receptor antagonist, decreased the low-frequency component of systolic (− 28%) and diastolic (− 40%) blood pressure. Losartan, added after HOE 140, induced a supplementary decrease of the low-frequency component (− 60% and − 42% for systolic and diastolic blood pressure). After the combined blockade, the low-frequency components of systolic and diastolic blood pressure variabilities of the hypertensive rats were equivalent to those of the control rats. Two-kidney, one-clip hypertension was also associated with an elevation of the mid-frequency component of the systolic blood pressure (+ 55%). The administration of HOE 140 did not change this component while losartan, alone or added after HOE 140, led to an increase (around + 100%) in mid-frequency oscillations of systolic blood pressure. The high-frequency oscillations of systolic blood pressure were increased by losartan in the two series of hypertensive rats. Losartan increased the mid-frequency component of heart rate variability in sham-operated rats while the heart rate variability was not modified during any of the treatment periods in two-kidney, one-clip rats. In conclusion, an increase in the low-frequency component of blood pressure variability was observed in a model of hypertension where the blood pressure is dependent upon humoral activities. The reduction of the slow fluctuations following the combined blockade of the kallikrein-kinin and the renin-angiotensin systems suggested the contribution of these humoral systems to this low-frequency component of blood pressure variability.