An elevated serum ferritin concentration recently has been shown to be associated with coronary artery disease and its risk factors, including blood glucose concentration. The purpose of this study is to establish the prevalence of elevated levels of serum ferritin in patients with non-insulin-dependent diabetes mellitus (NIDDM) without hemochromatosis and to determine whether or not deferoxamine is of therapeutic value in treating such patients. The level of serum ferritin was measured in consecutive eligible patients with NIDDM seen at routine outpatient visits. Five patients with an elevated serum ferritin were treated with deferoxamine, 1 g intramuscularly, twice a week for 12 weeks. The level of serum ferritin was measured every 4 weeks, and the level of glycosylated hemoglobin was measured at baseline, at the end of the treatment, and 12 weeks after treatment was completed. The level of serum ferritin was elevated in 34 of 102 (33%) patients with NIDDM. The level of serum ferritin remained elevated in 30 of 32 (94%) of these patients on repeat testing. In three of the five patients treated with deferoxamine, the level of serum ferritin was normalized, but no patient had an appreciable change in dosage of medication for diabetes or glycemic control. Non-insulin-dependent diabetes is a condition frequently associated with elevated levels of serum ferritin. Treatment with deferoxamine intramuscularly was not effective in improving control of glucose in our patient group.