A phase doppler anemometer (PDA) was used to measure axial components of mean and fluctuation velocities of air and particles in a pipe of 80 mm. inside diameter. Glass beads having mean diameter of 55 and 468 mum, respectively, were used, the density being 2590 kg/m(3). The fine particles suppress the air flow turbulence while the coarse ones increase it. Mixing fine particles with coarse ones in 5-9% in mass increases the turbulence above that by coarse ones alone. The acceleration pressure drop due to the particles is increased as well above that by the fine particles alone, which is larger than that by the coarse ones alone.