In the present study, gene-engineering producers for proinsulin and peptide fragments of glutamic acid decarboxylase (GAD), the main autoantigens of islet cells responsible for development of insulin-dependent diabetes mellitus (IDDM), were prepared. Basing on the obtained antigens. ELISA was developed to determine the autoantibodies in sera of patients. Sera from the following two groups of IDDM patients were studied: 1) adult patients with recently developed IDDM before insulinotherapy, and 2) adult patients with long-lasting IDDM with associated complications. Insulin/proinsulin antibodies were detected in 20% patients of group 1 and 41.7% patients of group 2. In sera from IDDM patients, antibodies to two GAD fragments containing amino acid sequences 1-80 and 151-585 were also detected. 16% of sera from patients with recently developed IDDM and 37.5% of sera from patients with long-lasting IDDM reacted with N-terminal GAD fragment. 12% of sera from group 1 and 45.8% of sera from group 2 reacted with central-C-terminal GAD fragment. The rate of sera of IDDM patients with detected antibodies in this study was some lower than that described in the literature.