The paper presents results of an experimental investigation of conveyed particles and carrier liquid velocities during flow of heterogeneous mixture in a vertical pipe. Measurements were carried out in hydraulic laboratory of Wroclaw University of Environmental and Life Sciences in transparent pipe of inner diameter D = 150 mm. Velocities of individual particles of different diameters were measured by radiometric method during vertical mixture flow. Goal of investigation was determining of slip velocities for the artificial nodules of mean diameter d ≈ 30 mm during the heterogeneous mixture flow in vertical pipe for mixture velocity range from 1.5 m/s to 3.5 m/s, mean volume concentration of solids was about 5%