1. A method of determining the risk of an individual who expresses Islet Cell Autoantibodies (ICA) of progressing to type I diabetes, comprising: a. obtaining a blood sample from the individual; b. preincubating the sample with purified glutamic acid decarboxylase (GAD) of the 65 kd form under conditions such that the GAD can form complexes with anti-GAD antibodies in the sample; c. contacting the GAD-preincubated sample with human or rat islet cells under conditions which allow uncomplexed ICA in the sample to bind to the cells; and determining the extent of ICA binding to the cells, wherein substantially complete elimination of ICA binding to the cells resulting from 65 kd GSD preincubation indicates that the individual has restricted ICA and the lack of substantially complete elimination of ICA binding to the cells resulting from 65 kd GAD preinccubation indicates that the individual has non-restricted ICA and a higher risk of developing type I diabetes.