As part of the revision of the Reference Man model of the International Commission on Radiological Protection (ICRP), we have reviewed and reanalyzed available data on blood flow and in previous publications have proposed reference values for total and regional blood volumes, total cardiac output, and the distribution of cardiac output. In this paper we unify these proposed features of the revised Reference Man within the framework of a dynamic blood circulation model and show how the model can be used to predict the distribution of decays of short-lived radionuclides after injection or absorption into blood. The total blood volume is partitioned into the blood contents of 24 separate organs or tissues, right heart chambers, left heart chambers, pulmonary circulation, arterial outflow to the systemic tissues (aorta and large arteries), and venous return from the systemic tissues (large veins). As a compromise between physical reality and computational simplicity, the circulation of blood is viewed as a system of first-order transfers between blood pools, but outflow from any given pool is delayed during the first pass of material through the circulation with the delay time depending on the mean transit time across the pool. The model can be used to predict the movement and gradual dispersal of a bolus of material in the circulation after intravascular injection. In contrast to the treatment of the circulation in ICRP Publication 53, Radiation Dose to Patients from Radiopharmaceuticals, the present model allows consideration of incomplete, tissuedependent extraction of material during passage through the circulation and return of material from tissues to plasma.