Interactions between the cardiovascular responses to the Valsalva manoeuvre and sustained handgrip were analysed in 5 men with untreated mild hypertension and 4 young normal subjects. Though set at a higher level, there was a normal blood pressure response to the Valsalva manoeuvre during concurrent sustained handgrip in 4 of the 5 hypertensive subjects. At the end of the handgrip period in which the Valsalva manoeuvres were performed, the blood pressure was higher and the heart rate lower than in the control period of sustained handgrip. The fifth subject developed a 'square wave' Valsalva response, which returned to a normal response when sustained handgrip was discontinued. Analysis of RR interval changes in the normal subjects showed that both the tachycardia during, and the bradycardia after, the Valsalva strain period were significantly reduced during simultaneous sustained handgrip. These results show that the two reflexes interact, but only to a minor extent, and that the baroreflex response is modified by sustained handgrip, rather than overridden as had previously been suggested. In view of the effect on the blood pressure and heart rate, subjects should avoid performing a Valsalva manoeuvre during sustained handgrip testing.