Thermodynamic properties of refrigerants are of great importance in the design and simulation of heat pumps and refrigeration units. The parameter values in the modified Benedict-Webb-Rubin equation of state proposed by Lee and Kesler (1975) have been determined for HFC134a with the Error-in-Variables Model. The types of data used for the parameter estimation have been : pressure-volume-temperature data for subcooled and superheated conditions, vapour pressures, saturated vapour and liquid volumes, isobaric and isochoric heat capacities and second virial coefficients. Calculations carried out with the equation of state according to Lee and Kesler, with the parameters here proposed, agree well with experimental data for the fluid.