An orthostatic circulatory load of varying degree (1-4 G) can be simulated by means of a human centrifuge. This results in a partial shifting of the intrathoracic blood volume into the capacity vessels of the lower extremity. In the pulmonary region, this is associated with a decrease in perfusion from the apical to the basal segments, which can be demonstrated by double nuclide perfusion scintigraphy. The degree of change in pulmonary perfusion was determined quantitatively in 26 volunteers by perfusion scintigraphy before and during acceleration, and the influence of dihydroergotamine (Dihydergot) was studied. The results show that the redistribution of the polmonary blood volume into the lower parts of the body can be largely prevented by Dihydergot. Pulmonary perfusion remains almost unchanged, compared with the initial value, up to an acceleration stress of 3 G, following intravenous injection of 0.5 mg dihydroergotamine. After oral administration (6 mg/d over 12 days), this applies to 1 and 2 G. Hence, dihydroergotamine represents, so to say, a "pharmacological anti-G suit".