In this paper we demonstrate a recursive algorithm to control the temperature profile of a batch reactor sustaining an exothermic reaction. The algorithm suggested here does not assume any prior knowledge of the detailed process, i.e., kinetics, etc. It, however, is different from generic black-box models as it uses an overall energy balance. This balance takes into account the different macroscopic effects, i.e., accumulation, heat generation, and heat loss. The heat generation rate H-gen(t) is estimated from the temperature trajectory and is used to generate a control law for isothermal operation. To achieve temperature control, the rate of heating or cooling was manipulated. The algorithm was successfully implemented experimentally to achieve the temperature control in the hydrolysis of acetic anhydride in a laboratory scale reactor. Heating of the reactor was done electrically and cooling by a coolant pumped by a refrigerated circulator. A PC-386 was used to measure temperature and send control signals. Isothermal operation was achieved by using this algorithm in a few iterations. We discuss how this control action can be used to design a composite controller. The control action is now taken independently by two controllers-one takes care of smooth but large changes in manipulated variable and the other small but rapid fluctuations (or noise) introduced by on line process perturbations.