Existing techniques for total hemoglobin concentration [THb] monitoring are invasive and cannot be used continuously and in real time. We developed and built a novel, light-weight (2 lb), low-cost, optoacoustic system for noninvasive, accurate monitoring of [THb]. The system incorporates an optoacoustic probe designed for sensitive probing of blood vessels with high signal-to-noise ratio at low energy of laser diode pulses. We developed a new algorithm for accurate monitoring of [THb] in the radial artery with this system. We tested the system in human subjects with different [THb]. The studies confirmed the capability of the system to accurately monitor [THb].© (2009) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.