It is generally assumed that the brain is not primarily involved in the development of a malignant hyperthermia syndrome (MH). However, spontaneous brain electrical activity (EEG) has not been related temporally to the development of haemodynamic, respiratory and metabolic changes during a fulminant MH crisis. In the present study cerebral blood flow (CBF) and spontaneous electroencephalogram (EEG) were recorded in 8 pigs susceptible (MHS) for the development of malignant hyperthermia and 8 non-susceptible pigs (nMHS) after exposure to 1% halothane. Power densities in selected frequency bands were calculated from the EEG. Additionally, body temperature and haemodynamic and blood gas parameters were studied over a period of 60 min. MH was triggered in all MHS animals. Following exposure to halothane initial EEG changes were noted after 20 to 30 min. They consisted of a decrease in total power and a shift to lower frequencies (delta-theta activity). At this time, CBF was significantly increased compared to control. In 4 animals an isoelectric EEG was noted at a PaO2 of 65-78 mmHg and PaCO2 of 52 to 64 mmHg. Characteristic changes for the development of an MH syndrome in haemodynamic and respiratory parameters as well as a rise in body temperature occurred after first EEG changes were seen. Our results do not support the hypothesis that early EEG changes during MH occur as a result of systemic hypotension, hypoxaemia, hypercapnia or cerebral ischaemia. Our data indicate that EEG monitoring in combination with monitoring of haemodynamic, respiratory and metabolic parameters may be of value for an early detection of an MH-crisis.