Sufentanyl is a new, potent, short‐acting, fentanyl‐like morphinomimetic. In the present study we compared the effects of high doses of sufentanyl and morphine on the peripheral circulation in β‐blocked dogs. Skeletal muscle surface pH (m‐pH) was recorded continuously as an index of the microcirculation. Sufentanyl (0.01 mg/kg) had no adverse effects on the peripheral perfusion. Morphine (4 mg/kg) caused a severe and rapid fall in m‐pH from 7.34 to 7.14 during the 30‐min experimental period. At the same time calculated blood volume decreased by 20%. This hypovolemic deterioration of the circulation was probably caused by a histamine‐mediated increase in capillary pressure and filtration of plasma from the intravascular space to the interstitial space. As sufentanyl could be safely administered to β‐blocked dogs, we recommend human studies. On the other hand, we discourage the use of high‐dose morphine anesthesia until human studies have proved that the collapse of the peripheral perfusion seen in this study