Diabetes, which causes enhanced oxidative stress, is a multifactorial disease that leads to deleterious effects in many organ systems within the body. Ubiquinones (coenzyme Q₉ and Q₁₀) are amphipathic molecular components of the electron transport chain that function also as endogenous antioxidants and attenuate the diabetes-induced decreases in antioxidant defense mechanisms. Insulin-like growth factor 1 (IGF-1) is considered to be an “essential surviving factor”, the level and function of which are compromised in diabetes. This study investigated the impact of IGF-1 supplementation on ubiquinone levels in a rat model of type I diabetes. Adult male Sprague-Dawley rats were divided into four groups: control, control plus IGF-1, diabetic and diabetic plus IGF-1. Diabetic animals received a single intravenous injection of streptozotocin (STZ, 55 mg/kg). IGF-1 supplementation groups received a daily intraperitoneal dose of 3 mg IGF-1 per kilogram body weight for 7 weeks. Coenzyme Q₉ and Q₁₀ levels were assessed by ultraviolet detection on high pressure liquid chromatography. STZ caused a significant reduction in body weight and an elevation in blood glucose level, which were not prevented by IGF-1 supplementation. In addition Q₉ and Q₁₀ levels in diabetic liver were significantly elevated. IGF-1 supplementation prevented liver alterations in Q₁₀ but not Q₉ levels. Q₉ and Q₁₀ levels in diabetic kidney were significantly depressed, and these deleterious effects were abolished by IGF-1 treatment. These data suggest that IGF-1 antagonizes the diabetes-induced alterations in endogenous antioxidants including coenzyme Q₁₀, and hence may have a therapeutic role in diabetes.