This study was conducted in Abbassia chest diseases hospital during the period between September 2000 to April 2001.The study included 50 patients complaining of chronic obstructive pulmonary disease during acute exacerbation of their illness which necessitate hospital admission. The patients were classified according to their ABG into two group:Group (1): Which includes 28 patients admitted to in-patients ward because of acute exacerbation of C.O.P.D. with normal or acceptable arterial blood gases.Group (П): which includes 22 patients admitted to respiratory intensive care unite [R.I.C.U.] due to acute exacerbation of C.O.P.D., and with disturbed arterial blood gases level.