This paper shows how a service process can be recast into a feedback control structure and how chemical process control principles can be applied. The outputs of the 'service plant' are process characteristics that meet the requirements of the plant's various stakeholders the manipulated and disturbance variables are those variables that are within and outside a service manager's control respectively; the model is a process flowchart; and the controller is the service manager. Good stability, performance and robustness are also required because customers value reliability, responsiveness, and consistency of service in the face of variations caused by involvement of people in the service delivery. To illustrate these concepts, a patient treatment process within an emergency ward was recast as a control system, and an off-line model-based optimal controller was applied to this stochastic process. The benefits of recasting services as feedback control systems flow both ways: service design and operation will be improved by the application of engineering principles; and chemical process control will benefit from techniques specially developed to handle market fluctuations.