A cardiovascular over-reactivity to stress may participate in the pathophysiology of hypertension. The aim of this study was to investigate whether baseline indexes of autonomic modulation of heart rate or baroreflex sensitivity were correlated with cardiovascular reactivity to stress. Spectral parameters of RR interval variability and the LF alpha-index were calculated in a resting condition in 53 untreated subjects (34 hypertensives; 19 normotensives). The reactivity to stress was expressed as changes of mean RR and systolic blood pressure during arithmetic mental stress testing. The cardiovascular reactivity was not correlated with either baseline spectral parameters of RR interval variability or LF alpha-index. In the multivariate analysis no confounding effect of diagnosis (hypertension vs normotension) was found. Moreover no interaction between diagnosis and both LF/HF ratio and LF alpha-index was observed. Thus, the cardiovascular response to a mental stimulus appears to prevail over the baseline pattern of cardiovascular regulation independently of the presence or absence of the hypertensive disease.