Acute hyperoxia (1 atm) in anesthetized dogs produced a 14% decrease in cardiac output relative to that observed with FIo2 = 0.21 and was associated with 7% decreases in heart rate and stroke volume. Changes in the distribution of peripheral blood flow during hyperoxia, as measured with radioactive labeled microspheres, included decreases in renal cortical flow (-20%), retinal blood flow (-27%), and blood flow to the caudate nucleus, mesencephalon, hippocampus, and cerebellum. Absolute blood flow to intestinal viscera, to respiratory and skeletal muscle, and to fat were unchanged. Simulation of these changes in cardiac output and distribution of blood flow using a digital computer model show a minimal change in the pattern of nitrogen gas elimination, with nitrogen partial pressures in the "slowest" body compartment within 1% of control by 60 min.