A tube system for collection of uncontaminated jejunal juice in children is described. It consists of an outer tube, the distal end of which is closed with a membrane, and an inner aspiration tube. When the outer tube is positioned at the site of aspiration, the membrane is perforated by applying air pressure through the outer tube. The tube was tested in 72 Danish children. With only one intubation having to be repeated, aspiration was achieved in all the children (95% confidence limits, 92.60-99.97%). The median intubation time was 10 min (range, 2-35 min). Mean time for aspiration of 1 ml of jejunal juice varied from 1 to 30 min (median, 5 min). The site of aspiration in the jejunum--expressed as the position of the tip of the inner tube--was from 0 to 6 cm distal to the ligament of Treitz (median, 3 cm). There were no complications.