Effects of a three-month exposure of both male and female rats under their development to lead acetate in drinking water on the hypothalamus-pituitary gland-thyroid gland-suprarenals and sympathico-adrenal systems were evaluated by determining noradrenaline (NA) in the hypothalamus and striatum, thyroxine (T4), 3,5,3'-tri-iodothyronine (T3) and corticosterone (CS) in the serum and catecholamines (CA) in both blood and suprarenals. NA in the hypothalamus and striatum was decreased in exposed males. CA in blood and suprarenals and CS in the serum were increased and NA decreased in the hypothalamus and striatum in exposed females. No serum T3 and T4 changes were found in males or females. The exposure to lead resulted in increased weight of spleen and kidneys in both sexes and suprarenals in females only. Weights of hypothalamus, striatum, liver and thyroid gland did not change. Female rats exposed to lead grew more slowly than control animals. Retardation in the growth was not statistically significant in males. The results indicate a specific stress reaction in female rats. In males only the sympathico-adrenal system seems to be affected by such lead exposure.