All disorders involve a disturbance of cellular and hence chemical function in the body. Rheumatoid arthritis (RA) is a chronic, systemic, inflammatory disease that usually attacks synovial joints and surrounding ligaments, muscles and their tendons and blood vessels. This article applies the concept of health professionals operating as external agents of homeostatic control (Clancy and McVicar, 20011a; 2011b) to RA and to the care of affected patients, using a case scenario to illustrate attempts to minimize homeostatic imbalances. After reading the article, nurses should be able to understand: how the principles of homeostatic theory apply to skeletomuscular function, in particular to synovial joint function; the skeletomuscular homeostatic role in movement; and that homeostatic failure of reduced mobility, as in RA, is a result of nature-nurture interaction; that illness arises from a cellular, hence chemical, homeostatic imbalance(s) (Clancy and McVicar, 2011a; 2011b; 2011c; 2011d; 2011e). RA is considered a cellular (B-lymphocyte) hence chemical (autoantibody) imbalance that causes the homeostatic imbalances (inflammatory pain, reduced mobility, reduced activities of daily living) associated with the condition. Health professionals are able at act as external agents of homeostatic control to only a limited extent when caring for people with RA because, as with any progressive disorder, they will only be managing signs and symptoms to improve patients' quality of life.