New hydrodynamic and heat transfer measurements are presented for two-phase slug flows in a reduced gravity environment. Air and two liquids, water and 50% aqueous glycerine were used to obtain a range of liquid Reynolds numbers from 1000 to 20,000 in a 25.4 mm i.d. tube. The measurements include void fraction, pressure gradient, and heat transfer coefficient. The enhancement of the heat transfer coefficient over single-phase liquid flow increases with increasing void fraction and is somewhat larger for the 50% glycerine solution than for water. Based on a comparison to normal-gravity correlations, the heat transfer coefficients are smaller at reduced-gravity than at normal-gravity under the same flow conditions. This can be explained by smaller liquid-phase turbulence levels in the absence of buoyancy-induced slip between the gas and liquid.