We investigated the impact of the scattering phase function approximation on the optical properties of whole human blood determined from integrating sphere measurements using an inverse Monte Carlo technique. The diffuse reflectance Rd and the total transmittance Tt ((lambda) equals 633nm) of the whole blood samples were measured with a double integrating sphere equipment. The experimental scattering phase functions of the highly diluted blood samples were measured with a goniophotometer. We approximated the experimental scattering phase function with Mie, Gegenbauer kernel (GKPF), and Henyey-Green (HGPF) phase functions to pre-set the anisotropy factor (mu) for the inverse problem. We have employed HGPF, GKPF, and MPF approximations in the inverse Monte Carlo procedure to derive the absorption coefficient (mu) a and the scattering coefficient (mu) s. The results show significant difference in the final estimates of (mu) s. 12© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.