Isothermal (vapor + liquid) equilibria of (4-methylpentan-2-one + pyridine + 1,4-dioxane) have been measured at (308.65, 313.15, 318.15, and 323.15) K using the total-pressure method. The pressure was also predicted using the Wilson model with parameters determined from binary (vapor + liquid) equilibria. The predicted vapor pressures agree satisfactorily with the measured values at all four temperatures. © 1990.