We studied the effects of increasing cardiac output by fluid loading on splanchnic blood flow in patients with haemodynamically stabilized septic shock. Eight patients (five female, 39-86 yr) were assessed using a transpulmonary thermo-dye-dilution technique for the measurement of cardiac index (CI) intrathoracic blood volume (ITBV) as a marker of cardiac preload and total blood volume (TBV). Splanchnic blood flow was measured by the steady state indocyanine-green technique using a hepatic venous catheter. Gastric mucosal blood flow was estimated by regional carbon dioxide tension (PRCO2). Hydroxyethyl starch was infused to increase cardiac output while mean arterial pressure was kept constant. In parallel, mean norepinephrine dosage could be reduced from 0.59 to 0.33 microg kg(-1) min(-1). Mean (SD) TBV index increased from 2549 (365) to 3125 (447) ml m(-2), as did ITBV index from 888 (167) to 1075 (266) ml m(-2) and CI from 3.6 (1.0) to 4.6 (1.0) litre min(-1) m(-2). Despite marked individual differences, splanchnic blood flow did not change significantly neither absolutely (from 1.09 (0.96) to 1.19 (0.91) litre min(-1) m(-2)) nor fractionally as part of CI (from 28.4 (19.5) to 24.9 (16.3)%). Gastric mucosal PRCO2 increased from 7.7 (2.6) to 8.3 (3.1) kPa. The PCO2-gap, the difference between regional and end-tidal PCO2, increased slightly from 3.2 (2.7) to 3.4 (3.1) kPa. Thus, an increase in cardiac output as a result of fluid loading is not necessarily associated with an increase in splanchnic blood flow in patients with stabilized septic shock.