The influence of short term anaesthesia with the N-methyl barbiturate Eunarcon(TM) on the pH and blood gases was investigated in 19 clinical healthy male castrated pigs of the breed Large White, three months old and with a mean body weight of 30 kg. The factors of oxygen in the blood - content, saturation of hemoglobin, O2 partial pressure - are diminished continuously during anaesthesia, with a decrease of pO2 on 77 % of the initial value. The pCO2 increased, and the peak value of 11 % above the initial level was seen already 10 minutes after starting the anaesthesia. The pH value like a seismograph of the ionic balance is not changed significantly. The results are discussed in connection with problems of medication and control of intravenous anaesthesia.