The results of an experimental investigation of the turbulent flow in a pipe roughened with hemispheres are reported. The roughness concentration was varied by changing the size of roughness elements which were uniformly distributed on the smooth boundary. Measurements included intensity of turbulence, macroscale of turbulence, Reynolds stress, mean velocity, pressure gradient, drag force, and shear stress on the smooth boundary. Turbulence and velocity measurements were confined to a vertical plane through the wake center line. The results of the experiments provide new information, and reduce some of the uncertainty about the structure of turbulence and mean velocity distribution in the wakes of roughness elements.