The microsphere method has been widely used for blood flow measurements in normal and tumour tissues. The microsphere method was evaluated for repeated measurements of cardiac output and regional blood flow in anesthetised rats and in anesthetised rats given noradrenalin and thereby having altered haemodynamics with special emphasis on liver blood flow. Comparing the microsphere method with the soluble indicator method (86Rubidium) gave equal cardiac output values. The liver blood flow was lower and the spleen blood flow was higher with the microsphere method. Two microsphere injections at 10 min intervals were performed on anesthetised rats. In one group 817 +/- 10(3) microspheres were injected each time, in a second group 436 +/- 10(3) and in a third noradrenalin was added and then 430 +/- 10(3) microspheres injected twice. There was good reproducibility for cardiac output and for most organ and tissue blood flows between first and second microsphere injection. No influence on arterial liver blood flow was seen. A blood pressure fall and a decreased heart rate was registered after the first injection in the group given 817 x 10(3) spheres. There was also a blood pressure fall in the group given noradrenalin after the first microsphere injection. The microsphere method with two injections of 436 x 10(3) microspheres seems adequate to use in arterial blood flow studies of the liver and simultaneous cardiac output measurements.