The role of adrenal steroids in antioxidant regulation is not known. Previously, we demonstrated some Coenzyme Q₁₀ (CoQ₁₀) alterations in pituitary diseases, which can induce complex pictures due to alterations of different endocrine axes. Therefore we determined CoQ₁₀ and Total Antioxidant Capacity (TAC) in pituitary-dependent adrenal diseases: 6 subjects with ACTH-dependent adrenal hyperplasia (AH); 19 with secondary isolated hypoadrenalism (IH), 19 with associated hypothyroidism (multiple pituitary deficiencies, MPH). CoQ₁₀ was assayed by HPLC; TAC by the system metmyoglobin-H₂O₂, which, interacting with the chromogenous 2,2^I-azinobis-(3-ethylbenzothiazoline-6-sulphonate), generates a spectroscopically revealed radical compound after a latency time (Lag) proportional to the antioxidant content. CoQ₁₀ levels were significantly lower in IH than AH and MPH, with a similar trend when adjusted for cholesterol. Also TAC was lower in IH than in AH and MPH, suggesting that adrenal hormones can influence antioxidants. However, since thyroid hormones modulate CoQ₁₀ levels and metabolism, when thyroid deficiency coexists it seems to play a prevalent influence.