Nine children with clinical diagnosis of glycogenoses were studied, types were confirmed through determination of levels and structure of glycogen, stimulation with glucagon and enzymatic defect analyses. Eight patients suffered glycogenoses type III and one, type VI. The major age group un type III was 1 to 2 years old (62.5%), the type VI was diagnosed in a preschool boy. Mean clinical features were: hepatomegaly, doll-like facies and short height. Major biochemical alterations were: transaminases elevation in both types, hypertriglyceridemia, hyperglycemia, metabolic acidosis and hyperuricemia only in glycogenoses III. One III type patient presented cardiovascular alterations. All patients showed increased concentrations of erythrocyte glycogen, with normal structure in type VI and abnormal in 75% of type III. Tree fourths of type III patients had a positive response to glucagon stimulation. No one presented glucose 6 phosphatase deficiency.