Noninvasive cerebral optical spectroscopy for monitoring cerebral oxygen delivery and hemodynamics. OBJECTIVE: To present an algorithm for noninvasive measurement of cerebral oxygen saturation (cerebral oximetry) and cerebral hemodynamics with near infrared spectroscopy. DESIGN: In vitro correlation of oximetry measurements with reference measurements; illustrative cases of hemodynamic and oximetric recordings. SETTING: Tertiary care neuroscience ICU. PATIENTS: Brain-injured patients with a prolonged, decreased level of consciousness chosen as illustrative examples. INTERVENTIONS: Two-channel multiple wavelength diffuse infrared transmission spectroscopy was interfaced with the scalp using adhesive. Transmission data were collected with gross superficial-to-deep spatial resolution. Saturation calculation based on the deep signal was observed longitudinally in the patient. With the same technology, arterial input and cerebral response functions, generated by iv tracer bolus, were deconvoluted to measure mean cerebral transit time. MEASUREMENTS AND MAIN RESULTS: A positive linear regression fit between diffuse transmission oximetry and measured blood oxygen saturation over the range 23% to 99% (r2 = .98, p less than .001) was noted. CONCLUSIONS: The approach used overcomes previously identified difficulties with cerebral oximetry, and demonstrates excellent in vitro correlation. The technique can be performed clinically without difficulty. A simultaneous measure of mean cortical transit time is possible. 