The authors performed biochemical examinations of twenty sheep's arterial blood and cerebrospinal liquor (CSL) to establish the changes caused by inhalation anaesthetics (halothane and isoflurane). Ten animals were anaesthetised by isoflurane (1.5 v/v%) and ten of them by halothane (1 v/v%). Blood samples were taken from a. femoralis and the CSL samples by lumbosacral punction before the anaesthesia (BA), during anaesthesia (DA) and after anaesthesia (AA). From the blood samples pH, pCO(2), pO(2) SAT and HCO3 ion and from the CSL glucose, Na, K and Cl ion-concentration were measured. There were no significant changes (p>0.05) during isoflurane narcosis except CSL glucose content, which was significant (p<0.05). During halothane narcosis pCO(2) and pO(2) DA (p<0.01), HCO3 ion DA (p<0.001), and AA (p<0.05) changed significantly.