Summary Changes in spectral analysis of the variability in systolic blood pressure (SBP) and heart rate (HR) were investigated in 12 normotensive volunteers during a well-standardized stress test. BP was measured indirectly from the finger by a noninvasive device (Finapres). The stress test was a computerized version of the Stroop color word conflict test (CWT). The influences of acute (single dose) β1-selective blockade by bisoprolol or angiotensin-converting enzyme (ACE) inhibition by lisinopril were analyzed by a double-blind placebo-controlled trial. During the placebo phase, the efficiency of the stress test was confirmed by a significant increase in SBP (25 ± 11% ). HR (36 ± 23%), and plasma concentrations of epinephrine (Epi, 54 ± 37%) and norepinephrine (NE. 27 ± 35%). Stress induced a significant increase in the amplitude of SBP and HR oscillations in the medium-frequency band (MF. 70− to 140-mHz range), which corresponds to the Mayer waves (27 ± 32 and 42 ± 43%, respectively for SBP-MF and HR-MF). The stress-induced increase in NE correlated significantly with the increase in HR (r = 0.68. p < 0.05). The stress-induced increase in SBP-MF correlated significantly with the increase in Epi (r = 0.69. p < 0.05) and in HR-MF (r = 0.69, p < 0.05). A significant decrease in SBP-MF at rest was observed with a single oral (p.o.) dose of bisoprolol, but not of lisinopril. As a noninvasive method, spectral analysis of the variability in SBP and HR may be of benefit in stress-induced modifications of the autonomie nervous system.