Laboratory measurements of the absolute absorption cross-section of CO, at the temperatures 295 and 373 K have been made between 200 and 206 rim using cavity ring-down spectroscopy. Below 205 inn, the cross-section at 373 K is significantly larger than at 295 K, whereas beyond 205 nm measurements at both temperatures yield cross-sections approximately equal to the Rayleigh scattering cross-section, within experimental error. The present measurements should resolve a long-standing discrepancy between previously published data on this system. (C) 2004 Elsevier B.V. All rights reserved.