Background : Environmental and genetic factors (viruses, toxins and diet) are involved in the aetiology of type 1 diabetes. Among the dietary factors, the role of breast feeding and exposure to cow's milk proteins deserve special attention. Aim: To determine the anti-BSA-IgG levels in type 1 diabetic children and to analyse the possible association with breast feeding duration, exposure to cow's milk and ß pancreatic auto-antibodies. Patients and methods: Blood samples were collected from 161 diabetic children and 144 controls to measure anti-BSA-IgG level, GAD65, IA-2 and ICA autoantibodies. All children answered a questionnaire about dietary habits during infancy. Results: anti-BSA-IgG was positive (using a cut off point of 25.6 ng/ml) in 98% of diabetic children and 0% of the control population. The length of breast feeding or early exposure to cow's milk did not influence the concentration of anti-BSA-IgG. Positive BSA titers did not increase the ß pancreatic reactivity (ICA+, GAD+, IA-2+). Conclusions: Our data confirm the high frequency of anti-BSA-IgG among diabetic children. However, a specific role in the immunological process of type 1 diabetes cannot be attributed to this protein (Rev Méd Chile 2003; 131: 865-72)