To investigate the function of HLA-class II genes in the autoimmune response of insulin dependent diabetes mellitus (IDDM), the HLA-class II gene of IDDM patients was introduced into Ltk- cells with pSV2-neo plasmid, using the calcium phosphate precipitation technique. We obtained a stable cell line expressing the HLA-class II gene from lymphocytes of IDDM patients. Expression was identified by direct ox erythrocyte-CrCl3-HLA DR monoclonal antibody rosetting.