The optical properties of white matter human brain, canine prostate and pig liver were measured in the wavelength range 330 - 1100 nm. The measurements were carried out in native as well as in coagulated tissues. We used the double integrating sphere technique to provide reflection and transmission measurements and a special homogenizing technique to prepare the tissue. The optical properties were evaluated using an inverse Monte-Carlo simulation, considering the geometry of the experimental set-up. All tissues show characteristic absorption bands at 420 nm and 550 nm, related to the strong absorption of haemoglobin. After coagulation the scattering increases drastically while absorption remains nearly unchanged. The anisotropy factor g increases with increasing wavelength and drops down slightly after coagulation. The wavelength behavior of tissue scattering has been compared with theoretical calculations (Mie-theory), showing that ideal spheres with an diameter between 0.6 and 0.8 micrometers fit best to the experimental results.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.