PaO₂ and PaCO₂ values were studied in 8 surgical patients with a modified Flagg can system anesthesia. Arterial blood gases were analyzed with a Radiometer before every induction, after the first 30 minutes of anesthesia and in the immediate post-anesthetic period. The following results were obtained: 1) The values of PaO₂ and PaCO₂ in all cases during anesthesia did not show any remarkable change. 2) In cases, with no necessity of muscle relaxation or assisted and controled respiration, especially in children, the modified Flagg can system anesthesia seemed to be safe, simple and economical.