The pancreatic duct or at least parts of this structure can be demonstrated today by sonography in 50-82% according to various authors. We have measured the caliber of the sonographically visualized pancreatic duct in 20 normal subjects after physiological stimulation with meal. The mean caliber of the duct markedly increased after meal. During dilatation a longer segment of duct is more clearly visualized. It is possible to document an increase of caliber of Wirsung duct "in vivo" as an evident sign of pancreatic secretion.