The impressive growth in the number of patients imaged with magnetic resonance (MR) technology has been accompanied by technical advances that have permitted more acutely ill patients to be studied with this diagnostic tool. Such patients, however, might require monitoring of vital functions during the examination. Unfortunately, the present construction of most MR imaging systems makes direct visualization of the patient difficult, if not impossible. Furthermore, the static and time-varying magnetic (and electric) fields associated with MR imaging systems may be incompatible with most physiologic monitoring devices, either because of safety or function. The authors review herein the data regarding presently available monitoring devices for various physiologic parameters and provide recommendations regarding what--and whom--to monitor during clinical MR examinations.