This paper presents a methodology for the selection of effective control structures for ternary distillation columns using only temperature measurements. A fundamental choice between controlling a single temperature or two temperatures must be made. If the former is selected, an additional choice between reflux-ratio control and reflux-to-feed control must also be made. The procedure discussed in this paper uses steady-state rating calculations to guide these selections. With product purities fixed (the impurity of the heavy key component in the distillate and the impurity of the light key in the bottoms), a steady-state simulator is used to calculate the required changes in the reflux flowrate and the reflux ratio as feed composition is varied over an anticipated range. For a ternary system, two "constant-purity" surfaces in two three-dimensional spaces are generated: (z(A), z(B), RR) and (z(A), z(B), R/F). The structure that has the flatter of the two surfaces should be selected if a single temperature control structure is employed. If neither surface is flat, dual temperature may be required.