Twelve clinically healthy dogs of both sexes (2-3 years age, 10-15 kg B.wt) were used in this study. The animals were divided into 2 groups (each of 6 dogs). Animals were anaesthetized by using single and repeated doses of thiopental by intravenous injection. From each animal two blood samples were collected before injection of anaesthetic solution and 24 hours after. Blood serum total protein, cholesterol, glucose, urea, creating, potassium, sodium, and chloride levels were estimated. Results revealed that intravenous injection of thiopental must be used only for induction of general anaesthesia. Complete anaesthesia could be reached by using the inhalation anaesthesia for prolongation the time of surgical stage more than one hour and to avoid its toxicity on the liver as well as on the kidnies.