A new apparatus for the measurement of excess enthalpies of liquid mixtures based on a Calvet microcalorimeter (C-80 Setaram) is described. Vaporization effects in the calorimetric cells are avoided by means of Viton balloons pressurized with nitrogen. Mixing is performed by precision-injection metering pumps connected to the cells by a piping system. The apparatus permits measurements in the range 25-130-degrees-C and up to 2.5 MPa for low boiling and highly viscous components. Results are presented for the water-glycerol system at 50-degrees and 80-degrees-C.