Many times at autopsy, on the basis of colour change of the stomach and intestinal mucosa, the forensic pathologist is able to suspect a particular nature of poisoning which leads to conclusive investigation of the case. An intense bluish discolouration of the gastric mucosa owing to capsule shell instead of the content is rarely encountered at autopsy. We report a case of fatal dextropropoxyphene poisoning, where gastric and small intestinal mucosa showed bluish discolouration owing to the gelatine capsule of the drug. Other causes of bluish discolouration of gastrointestinal tract mucosa at autopsy are also discussed.