Figure 1 Organotypic cultures of the two choriocarcinoma cell lines, JAR (A–J) and JEG (K,L), were grown in the absence (A,C,E,G,I,K) or in the presence (B,D,F,H,J,L) of 1 μM all‐trans retinoic acid (ATRA) in the medium. The experiments were duplicated for each cell line. Sections (40× magnification) were stained with haematoxylin–eosin (A,B), Ki‐67 (C,D), M30 (E,F), terminal deoxynucleotidyl transferase‐mediated deoxyuridine triphosphate nick end labelling (G,H), p53‐DO7 (I,J) and p21^WAF1 (K,L). An increase in apoptotic activity (B,F,H) and reduced proliferation rate (B,D) is seen after ATRA treatment. Reduced p53‐DO7 (J) and increased p21^WAF1 (L) expression can also be observed.