A theoretical model for predicting the forced convective boiling heat transfer coefficients of ternary mixtures is presented. The effect of mass diffusion near the gas-liquid interface is considered in both nucleate boiling and forced convection vaporization contributions. The predicted heat transfer coefficients are compared with experimental data, which are obtained for an HFC32 : 125 : 134a (23 : 25 : 52 wt%) mixture inside a horizontal smooth tube 6.0 mm i.d. and 4.0 m long, and in the ranges of heat flux 10-20 kW m(-2) and of mass flux 150-400 kg m(-2) s(-1). The present predictive method shows reasonable agreement with the experimental data within an accuracy of +/-30%.