A new method for determination of vapor-liquid equilibria in ternary systems is proposed, based on the following two relations.(1) The bubble point of the equilibrium liquid composition should be equal to the dew point of the equilibrium vapor composition.(2) The condensation point of the equilibrium liquid composition should be the bubble point of the equilibrium vapor composition. Using these relations described above, vapor-liquid equilibrium relations in ternary systems can be determined from the dew, bubble and condensation point data without the use of other assumptions. A new apparatus was designed for the simultaneous measurement of dew, bubble and condensation points. This apparatus makes it possible to measure dew, bubble and condensation points at any desired composition without analysis. Using the present method, vapor-liquid equilibrium relations were determined from experimental dew, bubble and condensation point data at atmospheric pressure for the ternary systems acetone-methanoUwater and methanol-ethanof-dioxane.