Gastric intramucosal acidosis, a sign of splanchnic tissue hypoxia, is common after cardiac surgery. We tested the hypothesis that an increase in splanchnic blood flow induced by dobutamine improves splanchnic tissue oxygenation after cardiac surgery. We measured changes in gastric intramucosal pH, splanchnic blood flow and oxygen transport in response to increased systemic flow induced by dobutamine (mean 4.4 (range 3.0-7.0) micrograms kg-1 min-1) after coronary artery bypass. We studied 22 stable postoperative patients who were allocated randomly to receive dobutamine (n = 11) or to serve as controls (n = 11). Dobutamine was given also to a separate group with a low cardiac index after operation (n = 6). The end-point was to increase cardiac index by at least 25% and to exceed 2 litre min-1 m-2. Dobutamine consistently increased mean splanchnic blood flow (control 0.6 (SD 0.2) vs 0.7 (0.2) litre min-1 m-2 (P < 0.05); normal cardiac output and dobutamine 0.7 (0.2) vs 1.1 (0.4) litre min-1 m-2 (P < 0.01); low cardiac output and dobutamine 0.4 (0.1) vs 0.7 (0.1) litre min-1 m-2 (P < 0.05)) and oxygen delivery (control 102 (29) vs 111 (28) ml min-1 m-2 (ns); normal cardiac output and dobutamine 106 (27) vs 156 (47) ml min-1 m-2 (P < 0.01); low cardiac output and dobutamine 75 (21) vs 110 (26) ml min-1 m-2 (P < 0.05)) but had no effect on splanchnic oxygen consumption (control 44 (10) vs 49 (10) ml min-1 m-2 (ns); normal cardiac output and dobutamine 45 (12) vs 51 (17) ml min-1 m-2 (ns); low cardiac output and dobutamine 37 (9) vs 40 (9) ml min-1 m-2 (ns)).(ABSTRACT TRUNCATED AT 250 WORDS)