We have evaluated the 133Xenon inhalation method for the determination of splenic blood flow. In twenty-two healthy persons the blood flow was on average 109 +/- 4 mg/100 g X min, which is equivalent to a total blood flow of about 170 ml/min. In patients with chronic fatty liver hepatitis specific blood flow was reduced (81 +/- 10 ml/100 g X min) as it was in patients with cirrhotic liver without splenomegaly (75 +/- 2 ml/100 g X min). With increasing weight of the spleen, the total blood flow rises, although specific blood flow is low. Our results obtained by the 133Xenon inhalation method are similar to results obtained by others using intraarterial injection of tracer gas. The advantages of the inhalation method as a non-traumatic method are: (1) the stress for the patient is very small; (2) blood flow measurements can be repeated within short periods of time. We consider for the present the 133Xenon inhalation method to be the method of choice for the determination of the splenic blood flow.