Treatment of carbon monoxide poisoning of a body by removal of a portion of the blood from the body, placing the portion in an exposure cell, exposing the portion in the cell to light of wave length and intensity that causes dissociation of carbon monoxide from hemoglobin, and returning the portion to the body. The intensity and wave length of the light is sufficient to dissociate a therapeutically-effective amount of carbon monoxide from the hemoglobin in the blood. The blood is circulated from and to the body through a concentric double lumen cannula. The wave lengths of the light are 540 and/or 570 nanometers. The cell exposes the blood to at least 9.5 Joules of dissociative light per milliliter of blood, and least 9.5 Watts of dissociative light per milliliter of blood per second. Oxygen is provided to, and the dissociated carbon monoxide is removed from the system.
