1) Fifty-three patients of good risk, aged between 24 and 64 years were utilized for this study. An analysis was made on respiratory-rate, -volume, tidal volume, expiratory CO(2)-content and blood CO(2)-content at F-O anaesthesia which was carried out in various mathodes; with 2% F-O for 25 minutes, or with 2% F-O for 5, 10 and 15 minutes followed by 1% F-O. One-half mg. of atropine was tried in some cases as preoperative medication. 2) In both cases of 2% F-O alone and 2% F-O followed by 1% F-O inhalation, an increased respiratory rate and, in contrast, a decrement of respiratory volume and markedly of tidal volume were observed. 3) Preoperative medication of atropine decreased such tendencies in grade compared with non-atropine group. It seems to be apparent that atropine preoperative medication acts against respiratory inhibition of Fluothane. 4) The changes of respiratory rate, -volume and tidal volume under 2% F-O anaesthesia can be slightly recovered at the switch over to 1% F-O anaesthesia. which is more noticed when atropine was used. The tidal volume, however, can not be recovered above the physiologically minimum level in any case. 5) The CO(2) content in expiratory air was observed to be increased as the anaesthesia was deepened, which was, to some extent, inhibited by atropine. The content in the end tidal air, however, always increased above the physiological level in all cases. 6) Although the blood CO(2) content was also increased by F-O anaesthesia, it was a little over the physiological limite of the variation. 7) Bennett assistor markedly inhibited the CO(2) contents both in expiratory air and in blood.