A new, concise nonlinear profile position observer using tray temperatures instead of tray compositions is proposed. Composition measurement has been one of the major difficulties associated with the composition control of distillation columns because the on-line analyzers still suffer from large measurement delays. high investment/maintenance costs and low reliability. One of common alternatives to the analyzers is to use the secondary measurement such as tray temperatures which is able to infer the tray compositions. The performance of the nonlinear control scheme which consists of this nonlinear profile observer and the model-based controller for profile position control of high-purity distillation column proposed by Han and Park (1993, A.I.Ch.E. Journal, 39(5), 787-796) has been tested and compared with that of Han (1993, Control of high-purity distillation columns using a nonlinear wave theory, Ph.D. thesis, KAIST) in simulation of high-purity distillation column. The results of this new control scheme is very similar to Han and Park (1993). The control scheme is insensitive to the noise of the temperature measurements and so simple that it can be directly applied to the real high-purity distillation columns. (C) 1999 Elsevier Science Ltd. All rights reserved.