Brain blood flow increased in the fetal lamb during morphine-induced stimulation of breathing. The increase in flow was 60% in the cerebral hemispheres and the cerebellum, and 100% in the midbrain plus rhinencephalon, pons, medulla and cervical spinal cord. Oxygen content of arterial blood decreased in all experiments and the arterial carbon dioxide tension increased in all but one of the experiments. The increase in cerebral blood flow observed is predicted by the changes in arterial oxygen content and carbon dioxide tension. Cerebral oxygen consumption and glucose utilization were not changed by morphine treatment. These results suggest that there is no direct effect of morphine upon cerebral blood flow and metabolism in the fetal lamb during morphine-stimulated breathing.