Two-phase flow pattern and friction characteristics for an air-water system in a 3.17 mm smooth tube are reported in this study. The range of mass flux is between 50 and 700 kg/m(2)s. The experimental data show that the two-phase friction multipliers are strongly related to the flow pattern. For a stratified-wavy flow pattern, a mass-flux dependence of the two-phase multipliers is seen. For a non-stratified flow pattern, the two-phase frictional multipliers are comparatively independent of mass flux. Correlations of the frictional multipliers are developed for stratified and non-stratified flow. To use the appropriate correlation in different regime, a simple criterion is proposed.