Renal blood flow in rats anaesthetized with the combination alphaxolone/alphadolone (3.90 mL min-1 (g tissue)-1) was significantly (P less than 0.05) greater than in rats anaesthetized with ketamine midazolam (3.24 mL min-1 (g tissue)-1, pentobarbitone (3.19 mL min-1 (g tissue)-1), fentanyl/fluanisone midazolam (2.84 mL min-1 (g tissue)-1) or urethane (1.99 mL min-1 (g tissue)-1). Renal blood flow in the urethane anaesthetized rats was significantly (P less than 0.05) lower than in animals anaesthetized with the other anaesthetic regimens, and is consistent with literature reports of a depressive effect of urethane anaesthesia upon xenobiotic renal clearance in the rat. Hepatosplanchnic blood flow was highest in the alphaxolone/alphadolone anaesthetized animals (71.7 mL min-1 kg-1), with the urethane anaesthetized animals demonstrating a significantly (P less than 0.05) lower (33.4 mL min-1 kg-1) blood flow. The fentanyl fluanisone/midazolam (65.4 mL min-1 kg-1), pentobarbitone (61.1 mL min-1 kg-1), and ketamine/midazolam (51.4 mL min-1 kg-1) regimens resulted in hepatosplanchnic blood flows of intermediate magnitude. The observed marked differential effects of the anaesthetic regimens upon renal and hepatosplanchnic blood flows may dramatically influence drug disposition in the experimental animal, and be of significance to laboratory pharmacokinetic studies in which anaesthesia is used.