Detection of interactions between light and tissue can be used to characterize the optical properties of the tissue. The purpose of this paper is to develop an algorithm that determines the reduced scattering coefficient (mus') of tissues from a single optical reflectance spectrum measured with a small source-detector separation. A qualitative relationship between mus' and optical reflectance was developed using both Monte Carlo simulations and empirical tissue calibrations for each of two fiber optic probes with 400-mum and 100-mum fibers. Optical reflectance measurements, using a standard frequency-domain oximeter, were performed to validate the calculated mus' values. The algorithm was useful for determining mus' values of in vivo human fingers and rat brain tissues.