A pulse oximetry system is provided in which LEDs of two different wavelengths illuminate tissue containing arterial blood flow. A photodiode receives light from the LEDs and produces electrical signals containing pulsatile components. The components of the two wavelengths are separated and the pulsatile waveforms are monitored until signal peaks are detected at the end of diastole. The waveforms are then integrated over the systolic interval, and the integrals are combined with the signal peak values to determine an index value. The index value is used to select a value representative of oxygen saturation from a look-up table.