OBJECTIVE: To establish a relatively simple,reliable and reproducible in vitro model of the blood brain barrier (BBB). METHODS: Cortical brain microvascular endothelial cells (BMEC) and astrocytes (AS) from 7-day-old rats were co-cultured in cell culture inserts.VIII-factor and GFAP immunocytochemistry were used to identify the cell types of the BBB model. Cell morphological changes were observed under light and transmission electron microscopes.At the same time, the BBB restrictive characteristics were assessed by ~(125) I-BSA permeability. RESULTS: The positive rates of BMEC and AS were 95 % and 99%respectively. The densely packed cells were observed and the characteristic BMEC 'cobblestones' were exhibited under the microscope on the 10th day of culture. Meanwhile a relative lack of pinocytic vesicles and the tight junction between the BMEC were presented. BMEC displayed a significant restriction of paracellular transport. CONCLUSIONS: An in vitro BBB model by co-culture with allogenic BMEC with AS was established, which was simple, reliable and reproducible as well as similar to the in vivo BBB in respect to morphology, ultrastructures and restriction characteristics.