Plasma concentrations of adrenocorticotrophin (ACTH) and cortisol were measured during insulin-induced hypoglycemia and lysin-8-vasopressin (LVP) test in 60 healthy subjects, non-smokers and habitually smokers of 10 or more cigarettes/24 hours. A marked and statistically significant rise of both hormones was found in non-smoker subjects, whereas smokers showed poor and not significant modifications. These results suggest that continuous chronic inhalation of nicotine may act as a powerful stimulus on the hypothalamo-hypophyseal structures that control the hypothalamic CRF and/or ACTH production and release. Central nervous mechanisms of hormonal regulation may become less sensitive and efficient when an acute rise of ACTH is required, as during stimulating tests. Our investigation confirms that cigarette smoking is heavily responsible of endocrine disorders, in particular of hypophyseal-adrenal axis.