To establish prediabetes in vitro model concerning the etiology of IDDM(Insulin Dependent Diabetes Mellitus) in cellular level we have designed prediabetes in vitro models in pa ncreatic beta cells. HIT-T15, RINm5F and isolated rat islets were chosen as pancreatic beta cells, and streptozotocin (STZ) used as diabetogenic agent. Degree of beta cell destruction to establish prediabetic in vitro model was determined by cell proliferation and insulin release using thymidine uptake and radio immuno assay. When HIT-T15 and RINm5F cells were treated with STZ, the degree of cell deterioration was dependent upon the origin and passage number of beta cells, and in the case of isolated islets STZ showed the more sensitivity than above two beta cell lines. The concentration and exposure time of STZ treatment to establish prediabetes in vitro model in beta cell lines and isolated rat islets were 2 ~ 10mM, 30 min. and 1 ~ 5mM, 30 min., respectively.