The relative orientations of carbon monoxide (CO) bound to and photodissociated from myoglobin in solution have been determined with time-resolved infrared polarization spectroscopy. The bound CO is oriented less than or equal to 7 degrees from the heme normal, corresponding to nearly linear Fe-C-O. Upon dissociation from the Fe, CO becomes trapped in a docking site that orientationally constrains it to lie approximately in the plane of the heme. Because the bound and "docked" CO are oriented in nearly orthogonal directions, CO binding from the docking site is suppressed. These solution results help to establish how myoglobin discriminates against CO, a controversial issue dominated by the misconception that Fe-C-O is bent.