AbstractThe mechanism by which all‐trans retinoic acid (RA) stimulates gap junctional intercellular communication (GJIC) in the rat liver epithelial cell line. IAR203, was investigated. When RA, at 0·1 μMfor 24–48 h, enhanced the dye transfer in IAR203 cells (× 1·4), it increased the amount of connexin43 (Cx43) in the cell–cell contact regions of the plasma membrane, as evidenced by analysis by Western blot and by immunofluorescence. It had no effect on the level of Cx43 mRNA. Freeze‐fracture analysis of the size of gap junctions revealed an increase of the proportion of small gap junctions in RA‐treated cells. We conclude that, in IAR203 cells, RA stimulates GJIC by acting at the post‐tran‐scriptional level of Cx43 regulation. The possibility that RA acts indirectly on the regulation of Cx43 expression, and increases the helf‐life of Cx43 by inducing adhesion mol