The technology for monitoring of NADH developed for animal study was applied to monitor patients who were exposed to various surgical procedures. The brain was the main organ monitored in neurosurgical patients who underwent vascular procedures or were treated in the ICU. Other organs such as the muscle, kidney, or urethral wall were monitored as well. Special devices and optical probes were developed and used in the early stage and were approved for use by the Institutional Review Board of the hospitals. In the last few years, our devices were cleared by the Food and Drug Administration (FDA). Typical results of the main reports are presented in this chapter.