Steviol glycosides, isolated from the plant Stevia rebaudiana (Bertoni) Bertoni, have been used as safe sweetening agents for more than 30 years. Beneficial effects of high doses of steviol glycosides on hyperglycemia and hypertension have been previously described when these abnormalities are present. This study was designed to evaluate the effects of steviol glycosides on blood glucose and on blood pressure (BP) in 3 groups of individuals. This was a randomized, double-blind, placebo-controlled, long-term study in three groups of patients: Group 1: subjects with Type 1 diabetes; Group 2: subjects with Type 2 diabetes; and Group 3: subjects without diabetes and with normal/low-normal BP levels. The subjects in each group were randomly allocated to active treatment (the steviol glycoside stevioside: 250mg t.d.s.) or to placebo treatment and followed-up for 3 months. Post-treatment systolic BP, diastolic BP, glucose and glycated hemoglobin (HbA1c) were not significantly different from baseline measurements, except for the placebo Type 1 diabetics group where a significant difference was observed for systolic BP and glucose. No side effects were observed in the two treatment groups. This study shows that oral steviol glycosides, taken as sweetener are well tolerated and have no pharmacological effect.