Cardiac output and liver blood flow were measured using 15-µm diameter radioactive microspheres in anaesthetized male rats 12, 24 and 48 h and 7 days after induction of acute renal failure with glycerol. Plasma urea concentration was greatest in those rats studied 48 h after glycerol injection and at 7 days animals could be divided into ‘recovering’ and ‘azotemic’ on the basis of plasma urea levels. Cardiac output was significantly lower at 12 h than that found in control rats, but it was significantly greater than control values in azotemic animals at 48 h and in the ‘recovering’ group of rats at 7 days. Changes in cardiac output did not correlate with alterations in haematocrit. Liver blood flow showed a number of changes in the azotemic animals relative to the control rats; at 12 h it was significantly lower in the glycerol-treated rats whilst it was increased at 48 h and in both groups of animals at 7 days. When the proportion of cardiac output distributed to the liver was determined using 50-µm diameter microspheres, it was not significantly different from that determined using the smaller microspheres at 12 and 48 h after glycerol injection. This indicates that the results with the smaller microspheres were not distorted by incomplete trapping in the hepatic and splanchnic vascular beds. The implications of altered liver blood flow for drug metabolism in renal failure