High lumbar epidural block was induced in seven dogs, causing a fall in mean arterial blood pressure (AP) from 24.5 +/- 2.9 to 12.0 +/- 3.1 kPa owing to reductions in cardiac output (QT) and systemic vascular resistance (SVR) to 67% and 68% of the pre-epidural values. Volume loading with dextran 10 ml X kg-1 b.w. increased QT nearly to the pre-epidural value. SVR decreased further to 61% of the pre-epidural value and AP was only slightly increased to 14.9 +/- 2.7 kPa. Subsequent administration of prenalterol 20 micrograms X kg-1 b.w. caused a further increase in QT to 17% above the pre-epidural value due to an increase in heart rate of 51 beats/min. AP did not change since SVR decreased further to 49% of the pre-epidural value. The hepatic arterial blood flow (QHA) was essentially unchanged during epidural block as well as during volume loading, while the portal venous blood flow (Qpv) was changed concurrently with (QT). In spite of the decrease in SVR, the preportal and hepatic arterial vascular resistances were not diminished following prenalterol. The increase in OT must therefore have favoured other vascular beds. Hepatic and pre-portal tissue oxygen uptakes were unchanged during the experimental procedure, while whole-body oxygen uptake decreased by 20% following the epidural block and increased nearly to the pre-epidural level following volume loading in combination with prenalterol.