Although there have been several reports of various self-tuning proportional-plus-integral (STPI) schemes and proportional-plus-integral-plus-derivative (STPID) schemes for controllers in recent years, their theory and practice are still immature. The capabilities of this type of controller to control real physical processes need to be proven in more detail. In this light, the paper presents an application of an STPI controller proposed by Cameron and Seborg (1983) to a microcomputer-controlled water bath system. The water bath is an example of an important component in many industrial chemical processes. Experiments are conducted to test the STPI controller and to compare its performance with two other controllers, namely a self-tuning controller (STC) due to Clarke and Gawthrop (1975, 1979) and a conventional PI controller. The reliability of the STPI controller is tested by artificially adding load disturbances, simulating a change in the process dynamics, and artificially adding a variable delay element in the control loop of the process. The results prove that the performance of the STPI controller is as good as a self-tuning controller with the added advantage of having a PI-like structure. Moreover, the STPI controller performs better than the conventional PI controller, especially when there are changes in the process dynamics.