50 patients were investigated during induction of anaesthesia and infrarenal aortic bypass surgery. 26 were operated on under neuroleptanaesthesia (NA group) and 24 under continuous epidural combined with a light general anaesthesia (epidural group). Blood losses were replaced with 5 per cent human albumin, red cell concentrates, and fresh frozen plasma. Ringer lactate solution was used to replace the functional extracellular fluid volume. During induction and maintenance of anaesthesia body temperature fell (NA group from 36.7 to 35.3 degrees C; epidural group from 36.7 to 34.9 degrees C) but no statistically significant difference could be found between the groups, in spite of better surface perfusion of the lower part of the body in the epidural group. The increase of plasma glucose concentration was lower in the epidural group as compared to the NA group. Stress mediated hypokalaemia was of the same degree in both groups, the median values of the plasma potassium concentrations being in the lower reference range (3.5-3.7 mmol X 1(-1], although large amounts of red cell concentrates were given. During clamping of the aorta a moderate compensated acidosis developed in both groups. Declamping caused a more marked increase of paCO2 and a greater fall of pH in the NA group as compared to the epidural group. Induction of anaesthesia was followed by a fall in oxygen uptake (NA group from 221 to 163 ml X min-1; epidural group from 230 to 189 ml X min-1) which appears to be delayed in the epidural group, with a short lasting statistically significant difference between the groups after eventration of the gut (NA group: 162 ml X min-1 less than epidural group 184 ml X min-1). Later on, oxygen uptake was equal in both groups, with no further changes due to clamping or declamping of the aorta. At the end of the operation, when nitrous oxide had been turned of, the oxygen uptake increased considerably in several patients, despite continuing artificial ventilation and intravenous hypnotics and analgesics having been given. Eventration and exterioration of the gut caused the most marked changes in haemodynamics and oxygen transport with significant differences between the groups. Immediately after eventration there was a sudden fall in paO2 in both groups (NA group from 99 to 83 mm Hg; epidural group from 96 to 84 mm Hg) and an increase of the calculated intrapulmonary right-to-left-shunt (NA group from 7 to 21%; epidural group from 10 to 19%).(ABSTRACT TRUNCATED AT 400 WORDS)