d-chiro-inositol (DCI) and manganese were administered orally singly and together to streptozotocin (STZ)- induced diabetic rats for 21 days and blood glucose values and body weights determined. At blood glucose values above 500 mg/dL, values were unchanged with DCI, manganese sulfate, or both over ten days. Insulin was administered to reduce the hyperglycemia to approximately 300 mg/dL. Over 12 days, DCI alone significantly reduced blood glucose (23%), and the combination of DCI and manganese sulfate reduced hyperglycemia even more effectively (40%) as compared to control animals. Of further interest, body weights both of female and male rats administered DCI and manganese were reduced, with females 25% compared to controls and males 21% compared to controls over the 21-day period. Metabolic mechanisms of actions of DCI and manganese to explain these results are discussed.