High quality optical components are of major importance for the development of new concepts and applications of carbon- dioxide lasers. Especially, as a consequence of the ever increasing output power of new laser systems, optical absorption has become a crucial topic for the production and commercialization of laser components. Therefore, activities for the standardization of optical absorption measurements were initiated in ISO/TC 172/SC 9/WG 6, which is dedicated to optics and optical instruments in lasers and laser related equipment. Recently, the corresponding standard document ISO/DIS 11551 on test methods for absorptance of optical laser components has passed the international voting procedure. For an evaluation of this standard practice, which is based on laser calorimetry, a round-robin test on optical absorption at 10.6 micrometer was started. In order to cover a broad range of carbon-dioxide laser optical components, different types of metal mirrors and transmissive ZnSe-optics were selected for the sample set, which was circulated between manufacturers and optical laboratories in the United States, the United Kingdom and Germany. This paper reports on the results of this experiment in respect to the new standard procedure described in ISO/DIS 11551. The contributions of the laboratories, which are based on a variety of different calorimetric measurement facilities, are compared and evaluated.