Earlier studies on metallothionein (MT) induction by stress used a wide range of stimuli, all of them considered as physical stressors. The present paper reports the effect of a basically psychogenic stress such as restraint on serum and liver MT. Male adult rats were stressed for 1, 12, 24 and 48 hours and then killed. Liver MT increased continuously throughout the experimental period. Rats deprived of water and food for 24 and 48 hours showed higher liver MT levels than control but lower levels than stressed ones. Serum MT was not modified by either restraint or water and food deprivation. The lack of relationship between the two MT pools was corroborated by the absence of a significant correlation between them. Restraint stress increased serum corticosterone but not glucagon levels, suggesting that only glucocorticoids are important in MT induction by stress. However, a strong circadian rhythmicity was observed in serum corticosterone but not in serum or liver MT in non-stressed rats. In addition, preliminary data with adrenalectomized rats indicate that glucocorticoids seem not to be essential in MT induction by stress. Likewise glucagon does not appears to be associated with MT induction by stress since its levels were not modified by restraint.