We have reviewed the literature to determine the value of C-reactive protein (CRP) measurements in the diagnosis and management of a wide range of conditions. CRP levels are of value in 6 clinical situations: (a) monitoring the response to antibiotic treatment in patients with known bacterial infections, (b) in obstetric patients with premature rupture of membranes, a rise in CRP can give early warning of intrauterine infections, (c) differentiation between active disease and infections in patients with systemic lupus and ulcerative colitis where the level of response to active disease has been previously established, (d) as a measure of disease activity and response to disease-modifying drugs in rheumatoid arthritis, (e) early detection of complications in postoperative patients, (f) in differentiating between infection and graft-versus-host-disease in bone marrow transplant patients. CRP levels have been used in an attempt to differentiate between bacterial and viral infections in various clinical situations, however the published literature does not support this role.