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SUMMARY Previous studies indicate that arterial baroreceptor modulation of heart rate is drastically reduced during static or dynamic exercise. We have investigated whether this reduction also occurs with regard to blood pressure modulation by the baroreflex. The study was performed in 19 subjects with uncomplicated untreated essential hypertension In whom blood pressure was measured intraarterially, and R-R interval was obtained by an electrocardiogram. The carotid baroreceptors were stimulated by neck suction of 30 seconds' duration, and equal stimuli were applied at rest and during hand-grip exercise performed at 40% of the subjects' maximal strength. Baroreceptor stimulation at rest increased R-R interval and reduced blood pressure. During hand-grip, the R-R interval responses to the baroreceptor stimulus were diminished by 61%. In contrast, the blood pressure responses were not significantly altered. Similar results were obtained when two subgroups of subjects with a lesser or greater degree of hypertension were separately considered. Thus, the carotid baroreceptor influence on blood pressure is largely preserved during exercise in contrast to the carotid baroreceptor influence on the sinus node, which is markedly impaired. 5 thus suggesting that the arterial baroreflex is impaired under these circumstances. This suggestion has not been supported by other studies, however. Bevegard and Shepherd* have observed that in normotensive subjects the hypotension induced by carotid baroreceptor stimulation is the same before and during dynamic exercise, and Ludbrook et al. 7 have also reported this in normotensive subjects during isometric exercise, although the heart rate response is simultaneously markedly reduced.There are two important implications in the studies above. First, the hemodynamic influences of arterial