Insulin-like growth factor-1 (IGF-1) reportedly suppresses the development of type 1 diabetes in NOD mice, suggesting that IGF-1 is possibly a candidate for the autoantigens in type 1 diabetes. We therefore examined the anti-IGF-1 autoantibodies (IGF-1 Ab) in sera from patients with type 1 diabetes using radioimmunoassay. However, we were unable to demonstrate the existence of anti-IGF-1 autoantibodies in type 1 diabetes with our method. Further study is necessary to clarify whether anti-IGF-1 autoantibodies are existent in human type 1 diabetes and to determine the significance of IGF-1 in the pathogensesis of type 1 diabetes.