The variation of gas velocity in the streamwise direction was measured for air and water flowing in a horizontal 9.53 cm pipe. Secondary flows are inferred from these measurements. At low gas velocities a stratified pattern with little or no entrainment was observed. Contours of constant velocity suggest the existence of two or more secondary cells, which create an upward flow at the walls and a downward flow at the center in the top part of the pipe. At high gas velocities and at large enough liquid flows, that entrainment is significant. droplet stratification causes a secondary pattern with downward flow at the wall.