The effect of vasopressin (AVP) on subcutaneous blood flow was studied by the 133Xenon wash-out method in 13 healthy subjects during three consecutive infusions of synthetic AVP, using increasing infusion rates. In seven of them, both subcutaneous and skeletal muscle blood flows were measured during the first infusion. The preinfusion, and infusion pAVP levels were 1.6 +/- 0.4, 3.4 +/- 0.4, 4.9 +/- 0.5 and 8.8 +/- 0.7 pg ml-1, respectively (mean +/- SE). The values are within the range normally found during dehydration. During the AVP infusions, the blood flow in subcutaneous tissues decreased 30-40% and the vascular resistance increased 60-80%. Neither heart rate nor blood pressure change significantly during the infusions. Plasma renin activity (PRA) decreased significantly. After cessation of the infusions, blood flow and vascular resistance rapidly returned to preinfusion values, while PRA increased very slowly. Skeletal muscle and subcutaneous tissues blood flows were found to be equally sensitive to small changes in the pAVP level. The present study has demonstrated that even minor increments of pAVP levels, as seen during dehydration, can significantly alter the regional blood flow in subcutaneous and skeletal muscle tissues in man.