The effect of ethanol (2 g/kg) on body temperature and catecholamine (CA) secretion in the cold (-20 degrees C) was investigated in adult male and female rats. The temperature dropped more rapidly in the females, being approximately 10 degrees C after 3 h as compared with 18 degrees C in the males. Controls received the same dose of ethanol but were kept at +20 degrees C. Increased concentrations of adrenaline (A) and noradrenaline (NA) were already observed in the serum and urine of the females after 0.5 h of exposure, but at 1 h in the males. Serum values were low in the females after 2 and 3 h and urine values high in connection with the deep hypothermic state. The urine values of the males were also high at the end of exposure, when they, too, were hypothermic. Depletion of amines was observed in the adrenals during the hypothermia phase, while CA concentrations tended to rise in the serum of the rats kept in the warm. The CA index (A:NA) was generally > 1 in both the serum and urine of the cold-exposed rats. The results show that female rats are less resistant to hypothermia than males, as indicated by their more rapid drop in body temperature and exhaustion of CA secretion. It is also apparent that urine CAs are worth measuring in cases of accidental hypothermia and possibly also other types of stress. An elevated CA index (> 1) seems to be an additional marker of hypothermia, showing a proportionally greater increase in the secretion of A than NA during cold stress.