ABSTRACTTwo groups of normotensive, male subjects having either a positive or negative parental history of essential hypertension were exposed to passive body tilt from horizontal to a 70° head‐up posture, while systolic and diastolic blood pressure, heart period, and respiration amplitude were sampled on a beat‐by‐beat basis. Subjects also performed mental arithmetic and cold pressor tasks, and cardiovascular reactivity was expressed as change from baseline levels. The body tilt data were analyzed by cross‐spectral analysis focusing on two frequency bands, one between .06‐.1 Hz, and the other at the predominant breathing frequency. The two groups did not differ significantly in their basal levels of physiological activity or in their response to the tasks. Cross‐spectral analysis identified tilt induced changes in the power spectra and coherence spectra within the two frequency bands. These changes differed between the two frequency bands and among the various physiological response systems investigated. Larger rhythmic oscillations in heart period within both frequency bands predicted greater cardiovascular reactivity to the mental arithmetic task but not the cold pressor task. The results are discussed in terms of neural control mechanisms (e.g., vagal tone) implicated in the dynamic regulation of cardiovascular function during psychophysiological states su