 Healthy subjects and cholestatic patients are enrolled in the study after giving informed consent. Control subjects with an indication for a gastrointestinal tract endoscopy within a cancer-screening program and patients with obstructive cholestasis with an interventional endoscopic retrograde cholangiopancreatography ERCP are included in this study. During endoscopy four biopsy specimens are obtained from the distal part of the duodenum. Biopsies are immediately stored at 70C until further processing. 