Organ blood flow was measured in eight spontaneously breathing male New Zealand white rabbits exposed to a 50 min period of asphyxia. The results were compared with eight control animals. Cardiac output and arterial pressure did not change. There was increased flow to the heart, brain and diaphragm. Flow to the kidneys and adipose tissue was reduced. Flow to the gastro-intestinal tract, liver, skeletal muscle and carcass was unchanged. Prolonged moderate asphyxia produces preferential blood supply to vital organs and maintains flow to the skeletal musculature and the gastro-intestinal tract; their blood supply is diverted mainly from the kidneys. These changes are similar to those seen in haemorrhagic and endotoxic shock in the rabbit.