The halothane test was performed under different conditions in 10 halothane-sensitive growing pigs (Landrace, line 01). Haematological and metabolic changes in blood were monitored during the handling of the pigs before the test, during the exposure to halothane and thereafter. Already in connection with the catching and fixation of the pigs, the levels of haemoglobin in blood, and of glucose, lactate and potassium in plasma increased significantly. However, the concentration of glycerol was not raised before the occurrence of the malignant hyperthermia. While the level of potassium decreased already from the beginning of the halothane exposure until the development of symptoms, the values of haemoglobin, glucose and lactate continued to increased. The level of the free fatty acids did not show any changes during the experimental period. An infusion of phentolamine reduced the increase of haemoglobin and potassium and an infusion of propranolol reduced the increase of haemoglobin and glycerol significantly, without any effect on the result of the halothane test. By an anaesthesia, starting 30 minutes before the exposure to halothane, the development of the typical halothane reaction was obviated for at least 10 minutes. Observed metabolic changes during a simultaneous epinephrine administration were exclusively due to its adrenergic effects.