Described is a development which combines the technologies of pulse oximetry and photoplethysmography for producing a monitor of Continuous and Non-Invasive Blood Pressure (CNIBP) and arterial oxygen saturation (SaO2), a complimentary combination which provides mutually reciprocal enhancements of one measurement to the other. The most significant of these enhancements is the improvement in accuracy and reliability of SaO2 measurements, provided by CNIBP data. This "pressure enhancement" to SaO2 has the potential for eliminating oximetric errors associated with reduced cutaneous blood flow; thereby opening the opportunity for practical noninvasive assessment of SaO2 in critically ill patients. The advantages of cost, reliability, and simplicity should render this combination unit competitive in the operating room where continuous SaO2 and CNIBP monitoring is a recognized need. The advantages of accuracy, reliability, and patient comfort should open up the intensive care market for noninvasive monitoring of SaO2 and CNIBP - a market area which so far has had little penetration by pulse oximetry. By providing quality monitoring of both SzO2 and CNIBP, this instrument would offer in many situations a practical alternative to the use of arterial lines and their associated risks.