Kangaroos and wallabies were anesthetized and cardiac output (Fick) and intravascular pressures were measured. These animals were found to be similar to other mammals with respect to serum electrolytes, hemoglobin, and blood volume. Intravascular pressures are largely comparable with other mammals; there is, however, a significantly higher systemic pressure and vascular resistance in the wallaby than in the kangaroo. There is also a difference in heart rate between the two species. Cardiac output, when corrected for surface area, is similar in the two marsupials and, on a weight basis, resembles that of the dog.