The paper contains a review of recent work by Process Systems Engineering (PSE) researchers in biomedical systems. The review is organised in the following four categories: analysis of systems corresponding to diagnosis of a condition, model simulation providing predictions resulting in a potential use for prognosis, design for an optimal action or set of actions based on a model and set of objectives which corresponds to devising a therapy, and operations where sets of patient data may be used to manage patient well-being or a disease condition. There has been work particularly in glucose regulation involving the liver system (the body's ‘chemical factory’), in the brain, in the pulmonary system, and to a lesser extent in some other parts of the body. There is evidence of useful proposed clinical outcomes. So far there is little evidence of clinical use of the results. There is a need for better models, handling of uncertainty to ensure conservative (and where possible guaranteed) predictions, and for greater interaction with the clinical community. There is real potential for much greater use of PSE approaches to these complex systems.