The explosion in computer use and technology during the past several decades has dramatically changed criti cal care. All vital signs can now be monitored accu rately, noninvasively, and continuously. We examined the predominantly noninvasive methods of monitor ing temperature, arterial blood pressure, heart rate and rhythm, respiratory mechanics, and gas exchange that can be used continuously on almost every patient in the intensive care unit. We conclude that temperature should be measured either intermittently with a rectal thermometer or continuously with a rectal, bladder, or great vessel thermocouple or thermistor probe. Arterial pressure should be measured either intermittently with a sphygmomanometer and cuff or continuously with an indwelling arterial catheter, except in specific situa tions when automated indirect monitoring may be use ful. Electrocardiographic rhythm monitoring has been clearly shown to improve prognosis in patients after acute myocardial infarction and should be universal in all intensive care units. Ischemia monitoring may prove beneficial, but its role has not been clearly defined. Re spiratory inductance plethysmography is effective in measuring respiratory rate, tidal volume, and breathing pattern. Pulse oximetry is useful in detecting occult hy poxemia. It should be continuous on most patients. Transcutaneous oxygen and carbon dioxide measure ment has a limited role in monitoring gas exchange and perfusion. Capnography also has a limited role in the intensive care unit but is more helpful in the operating room.