Turbulent gas-liquid stratified flow in near-horizontal, straight ducts with a regular two-dimensional wavy deformation of the interface has been studied. In this flow regime strong mean secondary currents have been observed. It was previously shown that these secondary velocities in the liquid phase may result from an interaction between wave pseudomomentum and mean axial velocity. In the present work also a model for turbulence-induced secondary flows due to anisotropy in the Reynolds stresses has been considered. For a wide duct case it was seen that the wave field model generated larger secondary flows than the ones induced by the turbulence model. However, the best agreement with the experimental results was obtained when the two effects were combined. For a more narrow duct the models indicated that waves and turbulence can be of equal importance in inducing secondary currents.