We studied 26 prepubertal patients diagnosed with type I diabetes mellitus and treated by both insulin and dietetic regime. They were analyzed according to their age. A morning blood sample was obtained after 12 hours of overnight fasting for endothelin determination (RIA from Nichols Institute) and HbA1c (Biorad). Patients were classified into two groups: 1) good control, with HbA1c values<8% and 2) poor control with HbA1c levels>8%