SUMMARY Investigations of the integrity and transport characteristics of 2/4/A1 cells have been done in this report. The cell line was isolated from rat fetal intestinal epithelial cells and transfected with thermolabile SV40 large T antigen. These cells proliferated at 33 °C, but eliminated the antigen and ceased proliferating at a non-permissive temperature (39°C). At 39°C 2/4/A1 cells started to differentiate but simultaneously the cells also underwent massive cell death. When cultured at 37°C these cells formed confluent and tight mo ....