The inhomogeneity of tissue structure greatly affects the sensitivity of tissue oxygenation measurement by reflectance NIRS. We have proposed a method for correcting the influence of a subcutaneous fat layer on muscle oxygenation measurement. In this study, this method was validated by measuring the peak-to-peak variation of muscle oxygenation in periodic exercise tests on the vastus lateralis and the falling rate of oxygenation in ischemia tests on the forearm. A newly developed multisensor probe with source- detector distances of 7-40 mm was used. THe probe, consisting of a two-wavelength LED and four photodiodes, was connected to a 4-channel tissue oxygen monitor. The fat layer thickness was also measured by ultrasonography. Results of the tests clearly showed that the presence of a fat layer greatly decreases the sensitivity of measurement and increases the light intensity at a detector. The correction factors of sensitivity were determined from this relationship and Monte Carlo simulation. The corrected oxygenation levels were quantitatively compared among subjects in spite of different fat layer thicknesses.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.