Figure 4 (A) Following 48 h culture with 100 μM of all‐trans retinoic acid (ATRA), immunohistochemical analysis has been performed using immunoperoxidase‐labelled cytokeratin (CK)8/18 with a haematoxylin counterstain. The epithelial surface and deep glands are strongly CK8/18 positive. At several places, the glands appear to have opened up and fused with the surface (arrows in 1, 2). (B) A CK8/18‐stained section through native Barrett's oesophagus is shown for comparison. The intensity of CK8/18 staining was always much stronger following ATRA culture. For A and B, the areas denoted by the black boxes on the low‐power view (×100 magnification) are also shown at ×400 magnification (boxes 1–4) to highlight the appearances at the surface.