Short-term fluctuations in blood pressure (BP) and heart rate (HR) were analysed in a group of twelve males with essential hypertension. Indirect finger BP was measured by a Finapres device. The effect of a 7-day administration of a cardioselective beta-adrenoceptor blocker, acebutolol (400 mg/day), was studied in a double-blind, randomized, placebo-controlled cross-over study. Compared with placebo, acebutolol caused a significant decrease in BP and HR. In addition, the standard deviation (SD) of BP and HR were reduced after acebutolol in the standing position. Spectral analysis of fluctuations in BP showed a reduction in the variability underlying the SD changes of BP and HR. This reduction predominated in the mid frequency (MF) region corresponding to Mayer waves. This effect was marked for HR since the MF component for standing HR after acebutolol was 46% the placebo level. The average reduction in MF component for standing Systolic BP (SBP) was 36%. No significant correlation was found between the Mayer wave reduction and the systolic, diastolic BP or HR lowering effect of acebutolol. No significant changes in the gain of the transfer function between MF SBP and HR fluctuations in the standing position were observed. The reduced MF component of HR and BP variability after acebutolol could be due to a peripheral cardiac and non-cardiac sympatholytic effect of chronic beta-adrenoceptor blockade.