An optical method has been developed by Emmerling, Meier, and Dinkelacker which allows the investigation of the instantaneous structure of the wall pressure field under a turbulent boundary layer. The main component of this method is a pressure transducer consisting of several hundred small elastic membranes, the displacements of which are recorded by interferometric means with a high‐speed camera. The method is explained and examples of measurements in a wind‐tunnel are presented. The measurements show the development and convection of pressure patterns of a wide range of sizes (from larger than one boundary layer thickness &dgr; down to 0.1 &dgr;) and with a wide range of convection velocities (from about 0.9U∞down to about 0.2U∞, withU∞the flow velocity outside the boundary layer). Some speculative considerations are made on what sort of flow configurations might be connected with the observed pressure patterns.