When jejunal juice is obtained by means of open pernasal tubes, the risk of the aspirates being contaminated is presumably high. The present study compares jejunal aspirates obtained from an open and from a closed tube system. Ten patients suspected of having abnormal jejunal flora and five healthy human volunteers were investigated. The pH values of aspirates obtained from the open tubes were significantly lower than the values registered in aspirates from the closed tube system, with a median difference of 0.70 (p less than 0.02). No differences between the two types of aspirate were registered with regard to total number of bacteria, number of bacterial species, lipase, total protein, total amylase or its fractions of pancreatic and salivary isoamylases. For the investigation of pH-sensitive substances in jejunal juice, a closed tube system is therefore recommended, whereas the use of such a device does not seem necessary for the study of bacterial microflora and pancreatic enzymes.