A patient with chronic schizophrenia, who had been treated for a long time with chlorpromazine, haloperidol, levodopa, benserazide hydrochloride, diazepam and biperiden, developed extreme hypothermia (about 32°C) when the dose of haloperidol was increased because of a deterioration of the patient's mental symptoms. No other physical manifestations were observed, except bradycardia. The turnover of noradrenaline in the cerebrospinal fluid and blood was increased in association with the hypothermia in this patient. A hypothesis about the involvement of monoamine imbalance in changes in body temperature is discussed.